HYDRODYNAMIC ANALYSIS OF DIFFERENT THUMB POSITIONS IN SWIMMING
The numerical simulation technique is currently one of the best established numerical tools in the field of biomechanical engineering. This methodology has been used in the computational analysis of the fluid flow in several research fields, such as medicine, biology, industry and sports (e.g. Boulding et al., 2002; Dabnichki and Avital, 2006; Guerra et al., 2007; Marshall et al., 2004). This numerical tool is a branch of fluid mechanics that solves and analyses problems involving a fluid flow by means of computer-based simulations. Thus, one of the major benefits is to quickly answer many 'what if?' questions. It is possible to test many variations to seek for an optimal result, without human experimental testing. The user is able to computationally model any flow field, provided the geometry of the object is known and some initial flow conditions are prescribed. This can provide answers and insights into problems which have been unavailable or obtainable with very expensive costs (using physical or experimental testing techniques). As such, numerical simulation techniques can be seen as bridging the gap between theoretical and experimental fluid dynamics. |
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Three-dimensional model Scanning Pre-processing Solving steady flow
In equations 1 and 2, V is the water velocity, CD and CL are the drag and lift coefficients, respectively, ρ is the fluid density and A is the projection area of the model for different angles of attack used in this study. Drag force is defined as the force acting parallel to the flow direction and lift force lies perpendicular to the drag force.
On the left side of the domain access (Figure 2), the x component of the velocity was chosen to be within the range of typical hand velocities during front crawl swimming underwater path: from 0.50 m·s-1 to 4.00 m·s-1, with 0.50 m·s-1 increments (Lauder et al., 2001; Rouboa et al., 2006). The y and z components of the velocity were assumed to be equal to zero. On the right side, the pressure was equal to 1 atm, a fundamental pre requisite to prevent the reflection of the flow. Around the model, the three components of the velocity were considered equal to zero to allow the adhesion of the fluid to the model. It was also considered the action of the gravity force (g = 9.81 m·s-2), as well as the turbulence percentage of 1% with 0.10 m of length (Bixler and Riewald, 2002; Marinho et al., 2008a). The considered fluid was water, incompressible with density (ρ = 996.6 x 10-9 kg·mm-3) and viscosity (μ = 8.571 x 10-7 kg/mm/s). |
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| RESULTS | ||||||||||||||
In Figures 5, 6 and 7 the evolution of the values of CD and CL according to flow velocity and angle of attack for each thumb position are presented. For the three thumb positions, CD and CL remained almost constant throughout the flow velocities tested (0.50-4.0 m·s-1). However, it was possible to note a slightly decrease in the force coefficients, especially from 0.50 to 1.50 m·s-1. |
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| DISCUSSION | ||||||||||||||
The aim of the present study was to analyze the hydrodynamic characteristics of a true model of a swimmer hand with the thumb in different positions using numerical simulation techniques. For the three thumb positions, the CD and CL remained almost constant throughout the flow velocities that were tested. A similar observation was already reported in other numerical studies (Alves et al., 2007; Bixler and Riewald, 2002; Rouboa et al., 2006; Silva et al., 2005). However, in the present study, a slightly decrease in the CD and CL were noted, especially from 0.50 to 1.50 m·s-1. Berger et al., 1995 and Bixler and Riewald, 2002 observed a similar tendency for lower velocities, in a towing tank experiment and using numerical techniques, respectively. For lower velocities, a very small decrease in the force coefficients values occurred with the velocity increase. However, from a practical standpoint, the coefficients were considered constant since the forces at these velocities are relatively small (Bixler and Riewald, 2002). The values of CD produced by the swimmer hand were very similar concerning the three thumb positions. However, the position with the thumb adducted presented slightly higher values at the angles of attack tested in this study. Moreover, the values of CL changed with the thumb position at angles of attack of 0º and 45º, although at an angle of attack of 90º the values of the different thumb positions were identical. At 0º and 45º, the position with the thumb fully abducted presented the highest values of CL. Although some differences in the results of different studies, it seems that when the thumb leads the motion (sweep back angle of 0º) a hand position with the thumb abducted into the plane of the hand would be preferable to an adducted thumb position. In this case, it is possible to suggest that during the insweep phase of the underwater path in butterfly, breaststroke and front crawl techniques and in the upsweep phase of backstroke technique the position with the thumb abducted could be gainful for swimmers. On the other hand, based only on the study of Takagi et al., 2001, when the little finger leads the motion (sweep back angle of 180º), during the outsweep phase of butterfly and breaststroke, and some parts of the downsweep phase in backstroke and upsweep in front crawl, the position with the thumb adducted seemed preferable. A possible explanation may be related to the change in the flow around the hand due to the thumb position: the lift force is enhanced by a pressure increase on the palm and a pressure decrease on the back of the hand (Colwin, 1992; Takagi et al., 2001). |
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Swim Stroke Pull Test: Treating Swimmer's Shoulder Bilateral and Anterior-Posterior Muscular Imbalances in Swimmers
Swim Stroke Pull Test: Treating Swimmer's Shoulder Bilateral and Anterior-Posterior Muscular Imbalances in Swimmers Ted Becker, Ph.D1 and Rod Havriluk, Ph.D2 1Everett Pacific Industrial Rehabilitation and 2Swimming Technology Research, USA Becker, T., & Havriluk, R. (2006). Bilateral and anterior-posterior muscular imbalances in swimmers. In J. P. Vilas-Boas, F. Alves, A. Marques (Eds.), Biomechanics and Medicine in Swimming X. Portuguese Journal of Sport Sciences, 6(Suppl. 2), 327-328. The purpose of this study was to determine the relative magnitude of bilateral and anterior-posterior differences in swimmers. Peak hand force was measured during aquatic exercise (horizontal arm abduction and adduction in a standing position) and swimming (freestyle and backstroke). The peak force values were significantly higher (p<.01) for exercise adduction than abduction and for the swim stroke with the arm in the adducted position (freestyle) rather than the abducted position (backstroke). The magnitude of the anterior-posterior difference was large for both exercise (1.5σ) and swimming (.8σ). Bilateral differences were trivial (.1σ, ns) in comparison. A training regimen that strengthens the arm abductors may not only decrease the incidence of injuries in all four strokes, but also increase hand force and, therefore, improve performance in backstroke. Key words: biomechanics, injury, technique, measurement, strength, evaluation Introduction: Bilateral imbalances are common in swimmers and can inhibit performance (6). Anterior- posterior differences are not only common, but also related to injuries such as shoulder impingement (2, 7). Muscular balance in the shoulder and scapula is necessary to avoid injuries (8). The ratio of land-based abduction to adduction strength was used to quantify anterior- posterior differences and was correlated to clinical signs of injuries in swimmers (1). The purpose of this study was to determine the relative magnitude of water-based bilateral and anterior-posterior differences in swimmers, relate these imbalances to complementary clinical screening procedures, and suggest related changes to training regimens. METHOD The subjects were 19 competitive swimmers (12 males and 7 females) between the ages of 14 and 17. The descriptive statistics for the males were: age (M = 15.4 yrs, SD = 1.4), height (M = 176 cm, SD = 7.9), and mass (M = 66.4 kg, SD = 9.9). The female data were: age (M = 15.4 yrs, SD = 1.4), height (M = 164 cm, SD = 7.5), and mass (M = 53.2 kg, SD = 5.4). Informed consent was obtained. Peak hand force was measured performing aquatic exercise (horizontal shoulder abduction and adduction in a standing position) and swimming (freestyle and backstroke) with Aquanex (previously described and validated in 5). For the aquatic exercise, subjects were instructed to perform five repetitions with maximum intensity. For the swim trials, the subjects were asked to sprint 20 m to a wall. Hand force data were collected over the last 10 m. Two trials of each test were performed with about 1 min rest. The single highest peak force value for each trial was used as the criterion. RESULTS Sample exercise and swimming trials are shown in Figures 1 and 2. Figure 1. Aquanex image of horizontal shoulder abduction/adduction exercise. Figure 2. Aquanex+Video images of freestyle and backstroke swimming. For aquatic exercise, the peak hand force values were significantly higher (p<.01) for adduction than abduction. For swimming, the peak hand force values were significantly higher (p<.01) for the stroke with the arm in the adducted position (freestyle) than in the abducted position (backstroke). Bilateral differences were not significant. The data are listed in Table 1 and graphed in Figure 3. Table 1. Peak hand force values (N), reliability coefficients (Alpha), and effect sizes (ES) for aquatic exercise and swimming. Figure 3. Peak hand force values for aquatic exercise and swimming. DISCUSSION The magnitudes of the anterior-posterior differences were large for both aquatic exercise (1.5σ) and swimming (.8σ). The anterior-posterior peak force ratios for aquatic exercise were similar to the values reported for land-based exercise (1, 4). The magnitude of these imbalances is less than ideal and can be related to performance restrictions and predisposition for shoulder injury. Muscular imbalances and injuries have been attributed to stroke mechanics, inadequacies in dryland exercise, and overuse (2, 3, 8, 9). Although these are substantial issues, a coach can address each one in a typical training environment. For example, a coach can first conduct a technique analysis to qualitatively assess the mechanical basis for muscular differences. The freestyle recovery of the swimmer in Figure 4 shows a bilateral difference in the angle between the upper arm and the horizontal. The restricted right shoulder position reflects a strength decrement in shoulder abduction. Figure 4. Stroke evaluation of freestyle recovery showing a smaller angle with the horizontal for the weaker right shoulder. Such qualitative clinical evaluations can also identify related structural conditions. Testing that mimics the stroke mechanics can show muscular imbalance/stabilization dysfunction. The Swim Stroke Pull Test (Figure 5) is a dryland replication of the freestyle arm motion. The swimmer’s hand directs force against the resistance of the examiner’s hand to imitate the propulsive phase of the stroke. Strength decrement in shoulder adduction can be determined by qualitative analysis of the swimmer’s force, body segment adjustments during the test, and video review. The scapular position for the affected right upper extremity shows dysfunctional elevation/protraction (Figure 6). Figure 5. Swim Stroke Pull Test. Swimmer is initially positioned with upper extremity at full shoulder abduction and then applies pressure to the examiners hand to complete shoulder adduction. Figure 6. Comparative demonstration of upper extremities completing the Swim Stroke Pull Test. Left upper extremity shows adduction position with no irregularities. Right upper extremity shows irregular position of the scapula and indicates weakness of the adductor function. Once a structural problem is detected, a coach can implement changes in the training regimen. Specific strength training that targets the associated abductors can be added to the program. An adjustment of total training distance and the proportion of frontal stroke (butterfly, breaststroke, and freestyle) to dorsal stroke (backstroke) distance may also be appropriate. CONCLUSIONS Muscular imbalances of considerable magnitude are common in swimmers. A thorough strategy for dealing with muscular imbalances includes a minimum of three components: evaluation, remedial strength training, and adjustment of training distance and stroke. First, it is important to evaluate anterior-posterior muscular differences either quantitatively or qualitatively. Second, additional aquatic and/or land-based strength training may be necessary. Third, it may be appropriate to reduce the total training distance for the frontal strokes and/or increase the proportion of backstroke. A training regimen that strengthens the arm abductors may not only improve muscular balance and decrease the incidence of injuries in all four strokes, but also increase hand force and, therefore, performance in backstroke. REFERENCES Beach M, Whitney S, Dickoff-Hoffman S (1992). Relationship of shoulder flexibility, strength, and endurance to shoulder pain in competitive swimmers. J Orthop Sports Phys Ther, 16(6): 262-268. Becker T (1982). Competitive swimming injuries: their cause and prevention. Paper presented at the American Swim Coaches Association World Clinic, Dallas, TX. Beekman K, Hay J (1988). Characteristics of the front crawl techniques of swimmers with shoulder impingement syndrome. J Swimming Res, 4(3): 15-21. Davies GJ (1992). A compendium of isokinetics in clinical usage and rehabilitation techniques. Onalaska, WI: S & S Publishers. Havriluk R (1988). Validation of a criterion measure for swimming technique. J Swimming Res, 4(4): 11-16. Havriluk R (in press). Analyzing hand force in swimming: three typical limiting factors. Am Swimming Magazine. McMaster W, Troup J, Arredondo S (1989). The incidence of shoulder problems in developing elite swimmers. J Swimming Res, 5(1): 11-16. Reeves T (1999). The role of the thoracic spine and scapula in the shoulder impingement. Paper presented at the conference of the International Society of Biomechanics in Sports, Perth. Yanai T, Hay J, Miller G (1998). Shoulder impingement in front-crawl swimming: I. a method to identify impingement. Med Sci Sports Exerc, 32(1): 21-29.
The Common Threads of Successful Swimming Technique
The Common Threads of Successful Swimming Technique
By Marshall Adams
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Introduction
Discussions presented in this paper are centered on the importance of the adductor muscles of the shoulder in all competitive strokes. The majority of examples cited are from the crawl stroke and butterfly, but the threads of common factors to success run through every stroke. The paper draws it conclusions from discussions of the core muscles of technique, the nervous system organization that provides the conscious and unconscious control of these muscles, the water that compounds the problem of movement within an unfamiliar medium, and the peculiarities of the shoulder joint that limits our movements. This unique view of human swimming propulsion draws upon principals, when analyzed in their entirety, that have profound implications for swimming instruction.
The progression of swimming since the beginning of the modem Olympic era has resulted in a variety of successful techniques performed within the parameters provided by the rules governing each competitive stroke. Much research and analysis has been conducted in order to explain the successes of the techniques used by the most successful swimmers. Yet, the search goes on to find the stroke techniques and scientific explanations that explain why one technique is superior to another. The variables involved with this analysis make the endeavor a difficult task. It is one thing to know the concept such as the potential of the shoulder's third class lever in human motion, but it is difficult to rate this factor, or anyone factor, with all the other variables involved in swimming success.
A common approach for success has been to try to emulate the techniques used by the world's best. It is in the techniques of the athletes that have broken the mold, and had success, that much insight into the technical truths is often revealed. This paper will discuss the factors that form common threads in successful technique and explore the truth revealed in the variables of success. It is understood that there is no magic bullet of technique perfection that results in success. However, superior technique is a key component in a champion's design for success.
The performances of Mary T. Maher in the late 70's and early 80's in the Janet Evan's 400 meters in the 1988 Olympics, in the 1992 Olympics, Grant Hackett's 1500 as well as Ian Thorpe's 200, 400 the competition and old records were left way back in the rear view mirror and shattered well beyond what could reasonably be expected. These people have broken the mold.
It is obvious to the casual observer that all the participants in the Olympic finals possess superior athletic body types and are highly trained and motivated. What may not be as obvious are the technique peculiarities that happen too quickly to be apparent or are obscured because they happen under water. It is apparent to this observer that the peculiarities of technique exhibited by the swimmers that have broken the mold and shattered records are observable and are significant components in these notable swims.
The Body Core
The ‘Body Core’ is the most current phrase used to describe what was written more then three decades ago by Charles E. Silvia to describe the importance of the large trunk muscles to producing efficient swimming motion. All body movement come from the contraction of muscle, but obviously, some muscles are more effective than others in producing efficient motion specific to a particular swimming stroke. The large muscles of the trunk are anchored to the central ‘core’ or the body and thus, the term ‘body core’ has some basis for its origin. The use of the term ‘body core,’ however, means little without defining the particular muscles involved with its application to technique. The ‘body core’ could easily be defined as the body’s trunk excluding the extremities and would include all the muscles both large and small attached to the trunk. Emphasis of the ‘Body Core’ that includes all of the muscles of the trunk for swimming would not be an efficient use of the most important muscles of the trunk. Thus, the use of the term ‘Body Core’ does not do justice to the particular muscles needed for emphasis, but rather loosely defines the important area from which these muscles originate. At least the coiners of the term ‘Body Core’ are in the right area to note where the most power originates for effective swimming propulsion.
The proliferation of materials and programs directed at the strengthening the body ‘Core’ has brought the area to the attention of swimming enthusiasts. However, the programs and exercises that are being promoted are not new and they are no more or less effective than they were 50 years ago. The use of medicine balls and calisthenics are a recycling of old methods, just as the knowledge of the ‘Core’s’ importance is an updating of old ideas, albeit not as accurate as first described. This is in reference to Silvia's identification of the primary muscles of shoulder adduction used in effective competitive swimming. No one can argue that the general conditioning of the body's core is detrimental. It can be argued, though, that general conditioning of the body's core is not the magic pill for success. Core conditioning is one piece of a training program puzzle, but without the specifics of muscle emphasis peculiar to the sport of swimming, no program of general body core conditioning will produce the desired swimming improvement.
The lack of precise definition of 'Body Core' as it relates to the effective muscles of shoulder adduction is not helpful to an athlete trying to learn how to use his strength effectively for a particular stroke. A good analogy would be the advice to a young child to use a utensil to eat ice cream when the spoon is what is most effective. An instruction to swim with the 'Body Core' is too general to have meaningful effect. General conditioning can never replace the exercise physiological law of 'Specificity of Training.’ Recruitment of efficient muscle motor units is specific to the task. The most important part of swimming training is the swimming and nothing can replace it. The so-called 'feel' for the water is actually the efficient recruitment of muscle fibers specific for the task Over recruitment of muscles by inefficient swimmers could be the result of non-specific training and/or the lack of specific training
The Muscles of the Body Core
The effective 'core' muscles for shoulder adduction used in all swimming strokes are the great trunk muscles that originate from the chest and back of the body (core) and have their insertions on the upper arm (humerus) bone. Many muscles originate from the chest and back but these muscles are the major adductors that work to bring the arm (humerus) in toward the mid-line of the body (adduction). The muscles include the latissimus dorsi, and teres major on the back (posterior) and the pectoralis major on the front (anterior). The teres major originates along the lateral boarder of the scapula, thus this important adductor muscle does not completely follow the definition of a core muscle since it does not arise from the trunk but arises from a bone that is close to the trunk. The scapula glides on the surface of the body's rib cage.
Why are these major muscles that for the most part originate from the 'body core' so important for effective swimming technique over and above other muscles which are also capable of producing or assisting in shoulder adduction? The answer can be found in the structure of the shoulder joint and the nature of these major 'core' muscles. These muscles are large, relatively powerful and are served well by the proximity of the heart's fresh blood supply. The use of the description 'relatively' has to do with comparing these muscles to the other muscles in the body. The shoulder joint itself is not a joint designed for strong movements in a 'relative' sense. The shoulder joint serves as the fulcrum for a third class lever system designed for mobility and speed of movement, not for strength. The latissimus dorsi, teres major and the pectoralis major muscles are the most powerful muscles associated with the joint. All three muscles work to pull the humerus toward the mid-line of the body as well as to rotate the humerus medially (internally). In all four competitive strokes the action of shoulder adduction is associated with the most propulsive phases of the stroke. Thus, the over simplified coaching instruction to 'swim with your core' has some basis in truth. (Relatively speaking)
The emphasis of certain muscles implies an unstated understanding that other muscles are not emphasized but are involved in an action. Fluid motion demands a synergy of action from all the parts that are moved. Very rarely does a muscle act alone and never in swimming. The large adductors of the shoulder have to work in synergy with the muscles of the arm, forearm and hand because the action of the shoulder adductors will move these segments whether their muscles are contracted or not contracted. Efficiency in a skill such as swimming demands that during the propulsive phase of the stroke the large muscles of the trunk be emphasized over the smaller muscles or the arm, forearm and hand. The larger muscles of the trunk are well supplied with blood, are involved with large movements and by their nature (relative sizes) able to tolerate large and repetitive workloads. The smaller muscles of the arm, forearm and hand are harder to supply with blood due to their distance from the heart and their relatively small sizes. It is apparent that if a movement can emphasize the larger and more vascular muscles for a repetitive movement, the more efficient the movement will be from both a strength and endurance standpoint. The only drawback to this idealistic technique description lies in the mechanical necessities of a particular stroke. This would include espoused techniques that require the fine manipulation of the smaller muscles of the arm, forearm and hand to produce stroke patterns deemed necessary for efficient propulsion.
Stroke patterns that emphasize more refined movements of the arm, forearm and hand add an increased energy cost for their application. A stroke with exaggerated out-sweeps, in-sweeps, up-sweeps and S patterns during the propulsive phase must rely upon muscles other than the great shoulder adductors of the trunk. The inefficiency of these small muscle actions is readily apparent to those who try to swim with these techniques. Any repetitive action that does not rely for the most part upon major muscle groups produces quick fatigue.
The challenge for the swimmer is to find the right synergistic applications of all the muscles involved in a stroke. The ideal stroke emphasizes the great adductors of the shoulder during the propulsive phase coupled with the optimum use of the small muscles of the arm, forearm and hand. The small muscles are used to position the extremity in its most advantageous propulsive position as it moves through the water in a particular stroke. The skilled swimmer makes this task appear to be easy because they do not over recruit muscles at inappropriate times and rely as much as possible upon the moving inertia of their repetitive and explosive propulsive phases to carry the stoke during the recovery and initial catch phases. They let the stroke carry them instead of working the stroke at the expense of their limited energy. This inertial and 'easy' stroke does require great muscular effort. Even the most 'natural' of athletes requires time to acquire the skill of an inertial stroke. The learning curve is different from athlete to athlete and the quality of the individual' s nervous systems that determines the ultimate degree of success in the acquisition of swimming skill. Michelangelo's ideal 'David' would not be a successful swimmer if he did not spend the specific time to learn the motor skill of swimming.
The Importance of Nervous System Organization
Efficient use of the 'body core' adductors of the shoulder joint during the propulsive phase of swimming is directly related to the organization of the human nervous system. Charles Silvia of Springfield College wrote about the difference between good and poor motor performance being determined by the quality of the sensory input. (18) Successful competitive performance, as stated in the last paragraph, is not possible without the ability to translate input (feel, touch, kinesthetic awareness) into effective motor output (recruitment of muscular force by the most appropriate muscles at the most appropriate times).
There is a paradox to this question for the successful acquisition of swimming skill. It lies in the understanding of the importance of the major core adductors of the shoulder and the difficulties involved with the tapping into their power. The nervous system is not organized to receive extensive sensory input from the major muscles of the trunk. The quality of sensory input from this area is limited in everyone. The organization of the cerebral cortex of the brain (motor and sensory homunculi) puts a distorted emphasis upon sensory input originating from the extremities and specifically from the hands and feet. The majority of the sensory nerve endings give input for motor control in the hands and feet, not in the muscles of the trunk. The sensitivity of the extremities is easily understood when comparing the results of injuries. A cut on the hand hurts much more than a similar cut on the shoulder. This lack of sensation from the area of the body core illustrates the paradox of body core emphasis. It is almost a “blind” move. The sensory information that arrives from the extremities is much more distinct to the processing brain than the information arriving from the body’s core muscles at the same time. The synergy of shoulder and arm/hand movement must rely upon sensory input coming from an area not directly associated with the muscles which produce the desired movement. The hands must provide the ‘feel’ while the major ‘core’ adductors of the shoulder provide the propulsive power.
The relative lack of sensory input from of the ‘body core,’ and more specifically the major adductors of the shoulder, could be used to explain the great variety of individual techniques. (Even by swimmers taught by the same instructors) It also points to the difficulties in teaching and learning swimming skills. Man’s presumptuous brain allows for creativity and variety regardless of a technique’s relative merits. Trout don’t vary their swimming technique; humans have the choice to decide their course of action. Humans, also, don’t have the experience of spending their whole existence in the water. The organization of the human nervous system makes it hard to learn how to emphasize the ‘core’ in an efficient manner, and water compounds the problem.
The Challenges of Performance in Water
Water immerses a swimmer in a liquid that envelops the body and gives no point of reference. Gravity is essentially neutralized. Down feels like up and back feels like any other direction. The sense of pressure exerted against the body is the same in all directions. Internal cues for successful technique are muted by the medium. Even the most sensitive areas for sensory feedback located in the hands and feet have no external reference point to base effective motor output. There is no cue of solid resistance indicating where and when to apply effective force. The laver system of the shoulder and arm provide an increased sense of resistance at the most inefficient positions in the stroke. An outstretched arm in the water is in its weakest mechanical position. Yet, without a solid reference point, a novice swimmer interprets the vigorous downward application of force, with the arm stretched out straight, as a helpful movement due to the added resistance caused by the weak lever position. The result is a bracing action with little propulsive component. The bracing movement feels forceful to the swimmer when, in reality, it is a weak and inefficient movement.
It is obvious that the world-class athlete has discovered the correct synergistic mix to produce the most efficient techniques. An analysis of the peculiarities of their individual techniques can reveal much about what is humanly possible. It is difficult to compare athletes of different eras beyond their inherent human qualities. But, as techniques have evolved there are similarities of technique that are universal because of the limits of movement defined by the rules of the sport.
Outstanding Performance Examples
The effective use of the body core and specifically the adductors of the shoulder joint has been a trait of many great freestylers in the recent historic past. One remarkable swim was the World Record and Olympic gold medal performance of Kieren Perkins in the 500 meters at the 1992 Barcelona Game. The under water television shots of the performance exposed Perkins' superior positioning of both arms as they assumed the initial catch position. This positioning movement put the forearm and hand in a position almost perpendicular to the surface of the water very early in the stroke. From this position Perkins maintained the forearm and hand in position perpendicular to the direction of travel throughout the most propulsive phase of the stroke as the shoulder adductors brought the humerus toward the mid-line of the body. The performance followed the kinesiological description of the ideal stroke first described by Charles Silvia in his 1970 book (18). Silvia's description was inspired by his study of 1956 and 1960 Olympic freestyle Champion Murray Rose. It was in the technique of Murray Rose that Silvia saw the potential of the shoulder joint to produce its most efficient swimming motion. Perkins' stroke, while not a mirror image of Rose's technique, clearly followed the same mechanical principles. Perkins coach John Carew, in an article for American Swimming Magazine the following year identified Murray Roses' stroke as the model for Perkins technique (2). This technique has to be considered one of the key factors in Perkins' dominating performance in 1992.
Identifying the Core's Importance Within a Stroke
Silvia's description of superior crawl stroke mechanics included four key parts upon which an efficient stroke depend:
1. Inertial shoulder girdle elevation and upward scapular rotation.
2. Shoulder joint medial rotation and elbow flexion.
3. Shoulder joint adduction and downward scapular rotation.
4. Inertial round off and release (partial supination of the forearm and hand and shoulder joint lateral rotation)(18)
The synergistic blend of all four parts of Silvia' s description is what the viewer sees in the performance of superior freestyle swimming. The application of part 3, shoulder joint adduction and downward scapular rotation, is the most propulsive phase. It is during this most propulsive phase that the core adductors of the shoulder joint contract vigorously against the resistance of the water to bring the humerus bone toward the midline of the body. A coach who instructs his swimmers to' swim with your cores' is telling his swimmers to emphasize point number 3 of Silvia' s 4-part craw stroke description. However, the emphasis of the core adductors is only effective during the propulsive phase of the stroke and any undue tension of theses muscles at different times in the stroke is detrimental to efficiency. Thus, the admonition of a coach for a swimmer to swim with his 'core' is too general to have positive effect if shoulder adductor muscle involvement is emphasized beyond the propulsive phase of the stroke.
The critical nature of Silvia's 3rd point of emphasis also might be used in the explanation of the great variety of successful crawl stroke techniques used at the world-class level Careful analysis reveal crawl stroke variations in current champions do not exist to any great degree during the most important propulsive phase of their strokes. The variations in technique come at times that are not critical to the ultimate propulsive efficiency of the stroke and can include the timing of the stroke; balanced recoveries, loping actions, catch up recoveries, straight elbow recoveries and kicking frequency. Olympic champion Brooke Bennett has been very successful without extending her elbows at the entry. Olympic champion Grant Hackett has been successful doing the opposite. Michael Klim exhibits a straight elbow recovery, as does Inge de Bruin. Ian Thorpe and Kieren Perkins can be observed using a bent elbow recovery. These non-critical variations come at times in the stroke that allow for great variation of action and thus, the discovery of the importance of the ‘core’ and specifically the great shoulder adductors is crucial. All of the aforementioned crawl stroke champions exhibit a vigorous and well-defined adduction and downward rotation of the shoulder that follows closely along the frontal plane of the body during the propulsive phases of their strokes. It should be noted that the total stroke must be considered in any evaluation of the shoulder without the accompanying and synergistic action of the other phases of the stroke. The three phases that comprise the release, recovery and catch leave room for individual variations due to their non-propulsive nature. There are however, kinesiological and mechanical parameters that must be followed during these stages that can affect the short-term efficiency of the stroke and the long-term integrity of the shoulder.
The shoulder can be put into a precarious position during the recovery and entry periods of the crawl and butterfly strokes. A straight elbow recovery tat does not externally rotate the humerus as the recovery progresses will result in an impingement between the coraco-acromial arch of the shoulder and the head of the humerus. Standing and trying to do a butterfly recovery with the palms of the hand facing backward limits the extent to which the hands can be raised above the head without encountering great resistance. An impingement can also occur in the front of the shoulder upon the reentry of the hand into the water after the recovery. This reentry shoulder impingement can occur if a swimmer uses a straight elbow entry with the shoulder fully flexed and abducted against the resistance of the water.
The identification of the proper application of the 'core strength' of the body and the associated implications of nervous system sensory organization is a positive step for anyone attempting to improve their swimming skill. It is within a synergistic application of stroke technique that the so-called ‘sweet spot' and 'zone' is revealed. World-class performance reveals to the observer the appearance of effortless grace. This apparent effortless grace is often misinterpreted as relaxation. An all out performance requires and demands vigorous muscular effort, but only during the most propulsive phase of a stroke. The other phases require a dependence upon the moving inertia generated by the propulsive phase and as little vigorous muscular action as possible to facilitate blood flow and recovery. A re1axed swimmer will go nowhere. The 'zone' has been attained when the results appear to be greater than the effort exerted. It is a familiar site to see an Olympic gold medalist appear to have more energy during the celebration immediately after their ‘all out’ performance. All four competitive strokes can be explored for the optimum use of the core shoulder adductors and the 'sweet spot' their proper application expose.
It is obvious to the informed coach that there are many factors which contribute to the ultimate outcome of efficient competitive swimming. Successful manipulation of the controllable variables is the greatest challenge for coach and athlete and allows for creativity from both the coach and the athlete and allows for creativity from both the coach and the athlete. However, the almost overwhelming number of factors governing success demands that a coach and swimmer filter out the trivial from the important. Successful swimming demands an economy of motion and the understanding of mechanics for efficient human swimming propulsion. Knowledge of the important role the shoulder joint adductors play in efficient swimming is useful for anyone attempting to increase his swimming skill. Shoulder joint adductors are at the 'core' of a champion's.
The differences in the approach to the entry and catch positions in two recent Olympic freestyle champions illustrate the successful variances in the non-propulsive phases. Brooke Bennett does not straighten out her elbows as the hand enters the water after the recovery phase. This action reduces the inertial lag time at the front end on the stroke and minimizes the possibility of shoulder impingement caused by the mistaken downward motion with the arm stretched out straight that was described earlier. Bennett quickly assumes the position of internal rotation of the humerus and spends no time flexing the elbow because it is never extended in front.
Ian Thorpe takes a much greater time setting up the propulsive phase of his stroke. From the point of hand entry until the hand releases and exits the water, Thorpe spends one half of that time with the hand and arm barely moving relative to his body. This huge inertial lag is more than compensated for by Thorpe' s efficient completion of the shoulder adduction movement of the opposite arm, complete shoulder girdle elevation of the arm entering the catch phase to insure a long stroke, and the increased propulsive emphasis attributed to his kick and the completion of the strong adduction movement of the opposite arm allow him to assume the catch position inertially with very little shoulder muscular effort. Thorpe, also, has the added anatomical advantage of extra large and flexible feet. It is from the stretched out straight hand entry position that Thorpe begins the catch and propulsive phases by flexing his elbow to about 90 degrees while internally rotating the humerus bone. No downward push at the beginning of the stroke is exhibited. The elbow remains shallow relative to the water surface even as the body rotates to promote breathing and/or the recovery of the opposite hand. It could be agued that Thorpe's added time of apparent arm inaction promotes a more efficient blood flow. thus adding another positive factor to balance the lack of propulsion during one half of the in-water phase of his stroke. Thorpe' s nearly stationary position during the entry phase accounts for approximately 1/3 of the total stroke cycle time Thorpe does not rush his stroke and his vigorous adduction of the shoulder does not begin until the hand and forearm have been positioned for the optimal use of the shoulder adductors during the propulsive phase.
The idea that world-class swimmers take the time to fine tune the pitch of the hand, search for still waters, sweep down, sweep out, sweep in, or sweep up during the propulsive phase of their strokes is not an accurate description of the stroke. These descriptive words suggest motions that will increase fine muscle involvement of the arm and forearm and deviate from the economically powerful adduction movement of the stroke's propulsive phase. These small muscle refinements are not the feature of the gross motor shoulder adduction movements exhibited by world-class swimmers during their propulsive phases. Adduction of the shoulder during the propulsive phase will appear to cause an outward and inward sweep of the arm as the arm rotates around the fulcrum of the shoulder joint. The vigorous and economic shoulder adduction movement only allows time for the maintenance of limb angles, and for the feel of water pressure against the hands during the propulsive phase. The sequence is true for both sprinting and distance swimming. Ideal shoulder mechanics are the same for both distances. Only the rhythm of the stroke (stroke frequency) separates the difference between efficient sprinting and distance technique. Ultimate competitive success at any distance using an efficient technique is limited by the other variables involved with success, not the least of which is the nature of the athlete’s muscular makeup, fast twitch or slow twitch muscle predominance. The example of Ian Thorpe’s successful world-class performance at distances covering the 100 to the 800 meters illustrates the universal effectiveness of one particular technique.
The strength and efficiency of shoulder adduction can be illustrated through the movement of the iron cross on the still rings in gymnastics. Although the iron cross position is a static gymnastic position, it demonstrates the most powerful and effective use of the shoulder adductors. All of the muscles of the shoulder, forearm, arm and hand are involved in the performance of an iron cross but it is the shoulder adductors that are the key to providing the support of the body’s weight. In swimming, it is the contraction of the great shoulder adductors that contribute most to moving the body’s mass. Thus, the importance of the shoulder adductors in both of these activities is in the strength they provide for support and movement of the body’s mass. Half way through the vigorous adduction movement in the crawl and butterfly strokes the action of the adductors is in a position similar to the mechanically superior position of the iron cross. The difference between the two activities is found in the difference between the static position of the iron cross and the ballistic results of the propulsive phase of the swimming stroke. Both activities use the most mechanically advantageous position of the shoulder joint to perform their skill. Swimmers also flex their elbows to increase the mechanical advantage of the shoulder’s 3rd class lever system. Deviation from the plane of the movements just described will result in the failure to hold an iron cross, or inefficiency of the swimming movement due to ineffective muscle angles of pull. An iron cross cannot be held with the arms held out straight in front of the body because the pectoralis major muscle is not at an effective angle to pull down on the humerus from this position. Adduction of the shoulder in swimming is not effective if the stroke follows a path that passes the same way as the unsuccessful iron cross. This would be a stroke that allows the hand to pull under the body.
The most important point to both Bennett’s and Thorpe’s strokes is the position they both assume with their arms that allows for a mechanically superior propulsive phase. This superior position maintains the forearm and hand in a position perpendicular to the line of travel for the longest possible time given the limitations of the shoulder joint.
Teaching Feel for the Core
A program to help identify the motion and feel for the effective use of these important muscles is the logical next step in the quest for improved swimming. The primary muscles of shoulder adduction don’t have the superior nervous input associated with the hands. It is thus, very helpful to give the area added focus through artificial means. The power of the shoulder adductors can be demonstrated through the use of an imagined or real prop. The object is an inflated balloon placed in the armpit. The objective of the demonstration is to pop the balloon. By popping the balloon in the armpit the swimmer can demonstrate the vigorous use of the primary adductors of the shoulder joint in a way that is similar to their action used against water resistance during the propulsive phase of the swimming stroke.
Completion of vigorous adduction effectively finishes the propulsive phase of the stroke because the major adductors are no longer in play at the end of adduction. Once the balloon is popped, the stroke should be redirected to enable an inertial recovery. Further pushing after the balloon is popped would not involve the prime movers of adduction. (The muscles used to pop the balloon) After the balloon is popped any extra effort to effect propulsion would necessitate the use of the smaller muscles of the arm and forearm. This action would add to the expenditure of energy at an inopportune time in the stroke and with inefficient muscles.
The illustration of the popping balloon underscores the concept of swimming with the body’s core and emphasis of the major muscles used to adduct the shoulder. In order to pop the balloon, it is the major muscles of the body’s core that are used to accomplish the task. The athlete can envision and feel the importance of adduction and the power of that movement. It is also easy to see the futility and ineffective nature of S curves and sweeping actions that use the smaller muscles of the arm and forearm to accomplish the task. A sweep or S curve stroke is not an effective way to pop the balloon. After the balloon is popped, effort to continue propulsion is ineffective because the major muscles of shoulder adduction are no longer involved. The so named ‘long’ stroke is the result of the completion of adduction that is set up by an early and efficient catch. Descriptions of long strokes that emphasize a push at the end of the propulsive phase and a finish with the hand past the hip risk the use of inefficient muscles of the arm and forearm and precarious shoulder mechanics.
The Economy of an Effective Propulsive Phase
The beauty of world-class swimming performance can be found in the economy of the movements the athletes exhibit. Extraneous and wasteful effort and movement are minimized. While the under lying mechanisms, physiology, and fluid dynamics are complex, the expression of the activity at the world-class level appears to be effortless and easy. Identifying the major propulsive muscles and demonstrating when they are most effective is a key step to efficient swimming. Prioritizing the focus reduces the complexity of a movement to a manageable state for conscience creativity.
Prioritizing the adduction movement is a key element in any stroke because the adduction of the shoulder is the most efficient movement of the shoulder during the propulsive phase. Adduction also sets up the other phases of the stroke by generating momentum that can be carried inertially through to the other phases. Stroke descriptions that emphasize movement that distract from the power of shoulder adduction and movements that occur at times in the stroke that occur during the non-propulsive phase are not helpful. Illustrations of such descriptions include sweeps, hip roll, and balance (to some degree). Body balance could be used to improve streamlining and resistance, but is a fine tuning event that follows well behind the mechanics of propulsion as a teaching priority. Hip roll is a result of an inertial, free-swinging stroke, but not an important focal point for propulsion. All strokes require vigorous adduction of the shoulder during the propulsive phases of the stroke and only two of the competitive strokes involve rotation around the long axis of the body (crawl stroke and backstroke). The lack of rotation of the hips along the long axis in the butterfly and breaststrokes does not compromise the effective adduction movement of the shoulder during the propulsive phases of these strokes.
The peculiarities of technique exhibited by world record holder and Olympic gold medallist Tom Dolan in the 400 IM in Sydney 2000 punctuate the importance of arm action over any other propulsive effort in his butterfly and backstroke legs of his performance.. Dolan took only one kick per arm cycle during his butterfly leg of this swim and used a two beat kick throughout his backstroke leg. Clearly, the arm action is the key part of Dolan’s propulsive effort in these two strokes.
Mechanical Risks of Shoulder Rotation
The strength and efficiency of adduction of the shoulder in swimming is not without its risks even in the most proficient of strokes. The vigorous adduction and shoulder rotation of the swimming movement can put the shoulder into a precarious position at the completion of the stroke and at the beginning of the stroke. As mentioned previously, the shoulder and the arm comprise a third class lever that is noted for its wide range of motion, not for its strength. Precarious positions that can result in injury can easily be assumed in the fast and repetitive motions of swimming.
The most notable precarious position of the shoulder during the crawl stroke is assumed during the hand entry. An impingement can occur in the front of the shoulder when the arm enters the water with the shoulder fully abducted, flexed and humerus internally rotated. From this hand entry position, if the swimmer’s first action is to push down, the result is a bracing action that is non-propulsive and serves to lift the body out of the eater. If the body is rotated on its long axis at the same time the hand enters the water, the result is an increase in the potential for impingement of the long head of the biceps and supraspinatus tendons. The result of this repetitive action is inflammation and pain as well as stroke inefficiency. The world-class swimmers that use a straight elbow entry reduce both the bracing downward push upon hand entry and shoulder impingement problems by internally rotating the humerus while flexing their elbows before any vigorous effort is exerted against the resistance of the water (adduction of the shoulder).
Another common trait of the straight elbow entry is the loping or catch-up nature of these strokes. The opposing and recovering arm is allowed to inertially catch up to the other arm as time is taken to position the propulsive arm. This catch-up action reduces the amount of body rotation on the long axis and further refutes the need to emphasize the perceived power of hip roll. The result of this action is a shallower stroke with the elbow of the propulsive hand remaining relatively close to the surface of the water even as the trunk of the body rotates on the long axis. The catch-up stroke forces less trunk rotation along the body’s long axis and negates the rotation of the body that would further aggravate the shoulder impingement upon hand entry.
Other precarious should positions occur in the stroke and illustrate the fragile nature of should rotation throughout the stroke. A swimmer who does not externally rotate the humerus during the recovery will limit the recovery due to the impingement of the greater tuberosity of the humerus with the coraco-acromial arch of the shoulder. Complete adduction of the shoulder at the end of the propulsive phase will wring out the long head of the biceps and the supraspinatus tendons. Vigorous extension of the elbow at the end of adduction forces the palm up and faces the palm away from the body during recovery. This action will result in prolonging the wringing out of the long biceps and supraspinatus tendons. While not effecting propulsion, these actions will ultimately impact the shoulder in a negative manner. The wringing out of the supraspinatus and biceps tendons creates an avascular situation in these tendons that Rathburn and Macnab have postulated overtime causes tendon degeneration (14). Couple the wringing out of these muscles at the end of the stroke and the impingement at the beginning of the stroke and it is no wonder that the syndrome of swimmer’s shoulder has been reported to be very common among competitive swimmers. It is for these reasons that a straight elbow recovery is fraught with danger. World-class crawl stroke swimmers have been very successful using straight elbow recovery techniques, but so have others been successful using the bent elbow recovery. The true key to propulsive success is in the completion of shoulder adduction that allows for a free-swinging and inertial recovery regardless of the position of the elbows during non-propulsive phases. The risk of a straight elbow recovery comes from the position in which the shoulder is subjected as recovery continues as well as extending the time the shoulder remains fully adducted at the finish of the propulsive phase.
Efficient butterfly stroke recovery demands a straight elbow recovery because being of the elbows require the shoulders to be lifted out of the water so the hands can clear the water. Freestyle allows for both a straight elbow and a bent elbow recovery due to the rotation of the body along its long axis. In both straight elbow techniques, (fly and crawl) risks to the shoulder come at the end of adduction of the shoulder that result in the ringing out of the supraspinatus and bicep tendons, and the shoulder impingement that will occur if the palms remain up as recovery continues. The success of bent elbow swimmers points to the frivolous nature of the push at the end of strokes. All actions at the end of the adduction phase of the stroke that promote a free-swinging and inertial (least muscular) recovery will have success. Muscular actions that promote the use of smaller muscles of the arm and forearm will have a negative impact on efficiency. Obviously, both the straight and the bent arm recoveries can be performed with minimal effort. An inertial straight elbow recovery requires a release of muscular tension at the end of the vigorous adduction phase and not an added push with the small muscles of the arm. An inertial flexed elbow recovery is initiated by releasing the grip on the water by supinating the hand and forearm while maintaining the flexed elbow of the propulsive phase this technique facilitates external rotation of the humerus by keeping the palm of the hand facing the body during recovery. Thus, the ringing out of the supraspinatus and biceps tendons is minimized to the extent that is possible at the end of shoulder adduction, and shoulder impingement during recovery is avoided.
The common threads of successful technique revolve around the ability of the athlete to exploit his power. This power is found in effective mechanics that emphasize the use of the shoulder adductors during the propulsive phase regardless of the stroke. Within these effective technique parameters are movements that are fraught with danger to the integrity of the shoulder. It is the understanding of these dangers that will allow for adjustments to individual techniques and continued exploration of the potential of human swimming. The future of swimming technique has been exposed in the recent performances that have broken the mold. The limits of performance have been moved into new territory and the exposure of the principles involved will allow for more athletes to experience the 'sweet spot' of outstanding performance.
Long distance session
WARM UP
900 snorkel
200 drill
16x50 shake build pace exp on 45s
200 loose
MAIN SET (Heart Rate Set)
400 150hr on 6.40s
300 150hr on 5.00s X4 (with no extra rest)
200 fast on 3.20s
100 fast on 1.40s
WARM DOWN
10x100 fins kick on 1.30s
4x200 pull on 2.45s
8x100 free I.M on 1.30s
300 swim down
De la puissance en crawl
Un article intéressant sur le sujet: source: http://www.theraceclub.net/columns/2008/05/swimming-with-your-body.html
Swimming With Your Body
By Gary Hall Sr.When Tiger Woods drives a golf ball well over 300 yards, he does so not simply by using or swinging his arms. He uses the power, weight and force of his entire body. It would be easier for him just to use his arms, but by unleashing the transferred power of his hips, core and shoulders moving through swing, the ball travels much further.
It is also easier for us to swim just with our arms and legs, as if they were attached to a surfboard. But our bodies are not surfboards. They behave more like bricks and require a tremendous amount of force to move rapidly through the water. We can generate some force purely from our arms and legs. In fact, one can usually generate enough force this way to get through 10 x 400 meters with short rest and still live to swim another day. This type of flat, paddling, mostly arm-and-leg-driven stroke is what we call the 'survival stroke'. It enables one to survive the long, punishing workouts, but not to swim fast...or at least as fast as one is capable.
To swim really fast, one must use more than the arms and legs. One must transfer the energy of the core of the body, including the shoulders, abdominals and hips into every arm stroke to maximize the power for speed. This does not happen naturally or easily. That's right. It takes more work and more effort to swim fast than slow. I am not talking about just pulling harder or kicking harder. I mean getting the entire body into the act.
So how do we do that? Mostly, swimming freestyle or backstroke with our bodies means rotating our shoulders from a near vertical position above the water on the recovery to a near vertical position below on the under water pull, while keeping the hips relatively flat. However, this rotation is not done slowly or casually. It must be done with force and speed. It must be done with conviction.
I often tell the campers who are learning the shoulder rotation for the first time, that one doesn't rotate the shoulders as if they are a rotisserie chicken on the grill. Rather, one must snap the shoulders from side to side, much like Tiger snaps his shoulders through the swing, following his hips. It is not just the degree of movement of the shoulders, but the speed of the movement of the shoulders that transfers more energy into propulsion. A bullet or torpedo moves down the barrel in a spinning motion and so we too must move down the pool by not turning, but snapping our shoulders from side to side.
Of the three fundamentals of fast swimming, the shoulder rotation is, for many, the most difficult to grasp for two reasons. First, most have been swimming flat like a paddleboard for so long that it seems very odd to be rotating the body. Second, it takes real work and a conscientious effort to swim with the body. Yet, to maximize your power for speed, shoulder rotation is essential.
Here is my favorite drill for freestyle or backstroke to learn how to properly rotate the shoulders. Have one arm outstretched over the head using a sculling motion with the hand. Kick flutter on your side with the other arm at your side but with the shoulder pointing straight up toward the sky or ceiling. Hold this position for at least 6 flutter kicks and with the head tucked down, but think mostly about having the shoulder of the trailing arm pointing straight up. Now take three consecutive freestyle (or backstroke) strokes with each stroke rotating the shoulder back to the vertical position. Now you end up with the opposite arm above your head and can think about getting the trailing shoulder vertical for another 6 kicks. This drill enables you to take the time to think about your shoulder position and to take 3 strokes trying to get the shoulder back into the same position. Once you feel you have this down, swim 2 lengths; the first drilling in this manner and the second swimming with the shoulder rotation, snapping from side to side. Obviously, the faster you swim the less time you have to get your shoulders turned, so the speed of the turn becomes more important. Also remember that the speed transfers more energy.
Another drill is to swim with one arm only, keeping one arm outstretched over the head sculling with the hand, while the other pulls with the shoulder rotating to the vertical on the recovery. One of the reasons I like the straight-arm recovery is that in order to recover with a straight arm, one has to rotate the shoulders to the vertical position. Biomechanically, the arm will not recover with the elbow locked unless the shoulder is rotated vertically. It just won’t work. Yet, once the shoulder is rotated vertically, it is actually easier to recover and creates less stress on the shoulder joint with a straight arm than with a bent elbow. Try it and you will see.
In the gym, put on a pair of boxing gloves and in front of the bag, hold your elbows at shoulder height and with the elbows bent about 45 degrees, hit the bag for one minute by rotating your shoulders from side to side, but not by bending the elbow. Hit it hard, like you are swimming the 50 meters, and rotate the shoulders as far as you can. This drill/exercise teaches speed and will also help strengthen the core muscles to achieve the shoulder rotation.
So now you have learned the 3 fundamentals of fast swimming.
1) Thick as a brick...which means use every trick in the book to help you streamline your not-so-streamlined body...especially keep your head down in freestyle. Way down!
2) Swim on the freeway...which means keep your hand out in front in the power position as long as you can and get them back there pronto! No stop-and-go swimming for you.
3) Swim with your body...which mostly means your shoulders and core, snapping from side to side to help drive you down the pool like Tiger drives his golf ball.
I have also suggested some drills that will help teach you these not-so-obvious fundamentals of fast swimming and will help remind you how to get them back if you should lose them. Do not underestimate the value of these drills to help you. Our World Team swimmers use them every day in practice. So should you.
Of course, the best advice I can give you is come down to Islamorada in the Florida Keys and spend some time with us. It will much easier for you to learn these fundamentals here than at home...and a whole lot more fun! See you soon.
Vidéo de Haydn Woolley
LE CRAWL....(2ème partie)
Après avoir expliqué dans la première partie, en quoi consiste réellement le crawl, c'est à dire une nage où le corps se meut en position uniquement horizontale en passant d'un côté sur l'autre, il faut maintenant appréhender l'avancement en crawl, c'est à dire la propulsion.
La plupart des manuels parlent du trajet sous-marin de la main et du bras sous l'eau. L'important est plutôt de chercher à comprendre que le corps va devoir passer au-dessus du point d'appui que va constituer l'appui de la main et du bras sur l'eau.
L'important est donc avant tout de sentir cette appui sur l'eau et de chercher par le mouvement entier du corps à passer au dessus de cette appui, le corps étant porté par l'eau.
Une fois la prise d'appui réalisée, le basculement du corps sur l'autre côté (à la recherche donc sa position horizontale de confort) va naturellement générer la force de propulsion sans qu'il soit besoin de forcer avec les bras et les épaules. Ce roulis qui va impliquer tout le tronc et notamment les muscles dorsaux va générer la propulsion.
LE CRAWL...(1ère partie)
1ère partie: la flottaison et l'horizontalité
Pas une séance de natation en piscine publique où on ne peut constater à quel point les nageurs s'évertuent à nager un crawl compliqué et contre-productif au prix de mille efforts !
Et si le crawl n'était pas plus difficile que cela ? Si le crawl était beaucoup plus simple qu'il n'y paraît à voir la manière dont tous ces crawleurs brûlent leur énergie pour arriver essouflés en bout de ligne ?
Pour s'en convaincre, il faut chercher à comprendre en quoi consiste réellement le crawl: de quoi s'agit-il en fait? le crawl est une nage où le corps se meut en position uniquement horizontale en passant d'un côté sur l'autre: au contraire du papillon ou de la brasse où le corps ne reste pas en position horizontale, le crawl lui n'implique pas de mouvement du corps en dehors de son axe horizontal. C'est fondamental de bien comprendre cela.
Cela a une double conséquence :
- le nageur doit bien maîtriser la position horizontale dans l'eau et il doit pouvoir la garder tout au long de la nage et
- le nageur doit être confortable en position horizontale sur ces deux flancs gauche et droit.
Si tel n'est pas le cas, le nageur va devoir en plus de générer une force vers l'avant générer les forces nécessaires pour tenir sur l'eau (en effet, si son corps n'est pas horizontal, il va agir comme une ancre dans l'eau!) et donc se fatiguer (en effet, s'il n'arrive pas à avoir une position confortable à l'horizontale à gauche et à droite, il va devoir utiliser une énergie importante pour tenter de maintenir cette position, cette énergie il ne pourra pas l'utiliser pour avancer plus vite).
La première clé du crawl est donc de maîtriser cette horizontalité. ll faut s'entraîner à flotter d'un côté puis de l'autre bien horizontalement de manière facile et confortable. On pourra constater que cela est possible pour tout nageur une fois la bonne position trouvée. Ensuite, il suffit simplement de rechercher à passer de la position horizontale confortable côté gauche à la position horizontale confortable côté droit.
Dans chacune de ces deux positions horizontales, on doit pouvoir ressentir un certain confort, un sentiment de relâchement presque: c'est une position que l'on doit pouvoir garder sans fatigue excessive. Ainsi crawler revient à passer d'une position confortable à une autre.
Dans cette position confortable:
- le corps est bien sûr allongé et horizontal; mais de face, il forme un angle avec la surface (cet angle est variable suivant les nageurs): de face, le nageur n'est pas à plat sur l'eau mais sur le côté.
- le regard fixe le fond du bassin, la tete est dans une position horizontale dans l'axe du corps (tout simplement dans la même position que lorsqu'on est debout),
- l'épaule est proche du visage : nous verrons que cette position a de nombreux avantages pour d'autres aspects du crawl (propulsion, pénétration dans l'eau),
- le bras est tendu droit devant dans une position variant du parallèle à l'eau à un angle (pas plus de 45°): idéalement, le bras doit être parallèle à l'eau; cela permet une allonge plus grande. Cela dit, mettre son bras dans cette position occasionne pour les moins bons nageurs d'avoir le bassin et les jambes qui plongent. Dans ce cas, il ne faut pas hésiter à prendre de l'angle avec ce bras pour éviter cette descente du bassin. Il est en effet fondamental de rester horizontal tout au long de la nage durant toutes les phases (y compris la respiration et la propulsion). Au fur et à mesure des progrès, il sera possible de remonter ce bras vers une ligne parallèle à la surface de l'eau. Mais cela n'est pas si important que cela et surtout beaucoup moins important que le maintien de l'horizontalité du corps en toutes circonstances.
Entraînez-vous en début de séance à travailler ces deux positions de repos à l'horizontal (sur le flanc gauche et sur le flanc droit), juste en avancant avec un léger battement de pieds sans même mouvoir les bras. Prenez conscience de la position de votre corps et cherchez à mémoriser les sensations pour ensuite les reproduire durant le crawl enchaîné.
Vous verrez c'est beaucoup plus simple qu'il n'y paraît. Pour apprécier si durant le crawl vous alternez bien ces deux positions, marquez un temps d'arrêt sur chaque flanc et vérifiez que vous vous sentez confortable et relaxé dans cette position, que vous pouvez la maintenir sans réel effort et qu'il vous est très facile de prendre votre respiration dans cette position adoptée sans avoir bouger le corps ou soulever votre tête: ce sera le signe que vous avez trouvé la bonne position. Vous devez vous sentir en parfait équilibre sur l'eau à cet instant. Si au contraire, vous sentez que votre corps est déséquilibré ou qu'il vous faut beaucoup d'effort pour le maintenir horizontal, ou que vous devez lever la tête pour respirer, c'est que votre position n'est pas la bonne. Recommencer l'exercice en répétant la recherche de la bonne position horizontale de chaque côté jusqu'à bien la maîtriser.
La plupart des nageurs qui se fatiguent en crawl sont ceux qui ne maîtrisent pas ces deux positions. Ils ne sont soit pas horizontaux dans l'eau, soit ils gardent leur horizontalité grâce à beaucoup d'efforts, ce qui les fatiguent inutilement.
les forces de propulsion
Dans son avancement, le nageur prend des appuis pour se propulser en suivant trois lois physique
1 - la 3ème loi de Newton (>pousser vers l'arrière fait avancer),
2 - le théorème de portance de Bernoulli (>exemple de l'aile d'un avion, elle a une basse pression au dessus et une haute pression en dessous) et
3 - le principe de godille de Counsilman (>déplacer une grande quantité d'eau sur une courte distance, en accélérant sur toute la longueur).
La glisse dépend donc bien de la vitesse, de la forme et de l'orientation du nageur.
source: http://blogs.univ-paris5.fr/hz05171/weblog/5432.html
Différents styles de crawl
1) Crawl classique dit en opposition
2) Crawl à l'australienne
3) Crawl TI
Mouvement du Crawl: décomposition
Les composantes d'un bon crawl:
voici dans l'ordre d'importance les composantes d'un crawl efficace:
1) l'horizontalité du corps: la première qualité à avoir est de pouvoir garder son corps bien horizontal dans l'eau. Si jamais le corps est incliné (le bassin plus bas que la tete), cela agit alors comme une ancre qui ralentit considérable le nageur.
2) la rigidité du corps: la seconde qualité à avoir est de garder son corps bien rigide (et principalement la partie du corps en les épaules et les cuisses). Imaginer un bateau désarticulé et comparer le à un hors bord bien rigide. Il est dès lors très important de penser à garder les muscles du ventre serrés lorsqu'on nage le crawl.
3) l'allonge : la troisième qualité c'est de bien se grandir dans l'eau: plus le corps sera allongé, plus la pénétration dans l'eau sera bonne. Image mentale: imaginer un ferry à fond plat et comparer le à un voilier de la classe America le plus affilé possible.
4) le roulis: la quatrième qualité c'est de nager en effectuant un roulis du corps en passant d'un côté sur l'autre. Ce roulis va permettre d'être plus fin sur l'eau, d'aller chercher plus loin la prise d'eau et d'utiliser les forces de pesanteur et d'archimède.
5) la réduction de la résistance frontale: la cinquième qualité consiste à chercher à réduire sa surface frontale d'avancement. Plus cette surface sera étroite, moins la résistance à l'avancement sera grande. Aussi il faut garder tête droite et chercher à avoir l'épaule avancée près du visage (presque à toucher la joue). Imaginer vous de face dans l'eau: il faut chercher à glisser dans un trou le plus petit possible devant soi.
6) la propulsion: la sixième qualité est l'efficacité de la propulsion. Pour beaucoup c'est la première qualité mais en fait c'est faux car si jamais vous n'avez pas préalablement les 5 qualités précédentes, vous gaspillerez une force considérable pour vous propulser dans l'eau. La propulsion est très importante; néanmoins comme le démontre un style de crawl que celui de Total Immersion (TI), la force nécessaire pour la propulsion peut être relativement réduite; si l'on cherche une propulsion puissante, il faut décomposer le mouvement en 4 phases:
- allongement du bras dans l'axe de l'épaule avec avancement de l'épaule en avant et prêt du visage (recherche de sensations: "étendre le bras bien tendu et bien haut comme un enfant qui demande la parole en classe"). L'épaule ainsi fixée, la main se tourne légèrement vers l'extérieur et le coude se plie jusqu'au maximum à angle droit (l'angle peut être plus ouvert) ;
- mouvement du bras en arc de cercle autour de l'épaule (levier du bras sur l'axe de l'épaule) sur la ligne horizontale du corps (en gros mouvement des gymnastes en croix de fer aux anneaux) ; du fait de ce mouvement, la main trace un "I" dans l'eau allant sur une ligne parallèle à la ligne d'avancement du nageur ;
- fin du mouvement le bras se détend: il n'est pas nécessaire d'étendre complétement le bras durant la phase finale.
En dernier lieu, un mot sur le battement. Pour un amateur, le battement n'est pas à négliger mais en prenant en compte qu'il n'a pas véritablement de rôle de propulsion mais simplement d'équilibrage du corps et de la nage.
Thoughts on the crawl stroke
By MARSHALL ADAMS
Why are the Australian men making such incredible advances in freestyle events from 200 to 1500 meters?
It is a result of the outstanding application of an old technique applied by superior athletes who are well-trained and highly motivated.
The outstanding performances by the Australian men's freestylers in recent years have elicited much speculation as to how they are accomplishing such feats. The most recent world records by Ian Thorpe in the 200 and 400 meter freestyles are the latest testaments to the strength of freestyle swimming by Australians.
The Aussie men now own the world records in all of the freestyle events from 200 to 1500 meters. And with Alex Popov now living and training in Australia, it could be argued that the Land Down Under is the place to be if freestyle success is your quest.
What is it that has separated the Australians from the rest of the world in the crawl stroke?
I believe the Australians are using an old technique first performed by Murray Rose in the 1950s and subsequently described by Charles Silvia in kinesiological terms. It is the outstanding application of this technique that is obvious when viewing the underwater video of these great Australian freestylers. Speculation about the rest of the world's lack of competitiveness with the Australians could center upon the peculiarities of Australian technique. And it is my belief that it is Australian technique that is the major reason for Australian dominance in freestyle events.
The excellent underwater videos taken at the Barcelona Olympic Games showed Kieren Perkins' superior stroke technique while he was setting the world record in the 1500 meter freestyle. It was then that I noted the similarity between the technique of Perkins and the technique of Murray Rose. After the Games in an article in American Swimming Magazine, Perkins' coach, John Carew, stated that Perkins' stroke is based on the stroke of Murray Rose. The evidence that this technique is superior is compelling. Perkins has swum 20 seconds faster than any American for 1500 meters. And the only challenge to Perkins' superiority has come from his own national teammates.
But the performances such as Perkins' are often dismissed as freak events. Bob Beamon's long jump at the Mexico City Olympics or Mary T. Meagher's 200 meter butterfly in 1981 are examples that come to mind. These athletic performances were so superior to the rest of the world that the competition seemed to be playing a different game. Add to this the most recent world record performances of Ian Thorpe in the 200 and 400 meters plus the dominance of the male Australian 4 x 200 relay, and a pattern of individual superiority, as well as team depth in Australia, begins to emerge.
Obviously, many factors can contribute to superior performance. Thomas Cureton identified four factors that together determine athletic success. These factors include training methods, body types, the determination of the athlete, as well as technique. It is not the purpose of this article to belittle the importance of training methods, body types and determination of the athlete in producing outstanding results. Certainly, the Australians possess outstanding programs and superior motivated athletes. And their other stroke specialists are also competitive at the world-class level. But it is in the male freestyle events of 200 to 1500 meters that the Australians are dominating. The dominance of so many events, by such significant margins, in the most common of strokes has to raise the eyebrows of swimming coaches everywhere.
Charles Silvia described the great Murray Rose's stroke as possessing four distinct parts that together formed a stroke that was humanly mechanically superior. The "Big Four," as Silvia named it, are:
- Inertial shoulder girdle elevation and upward scapular rotation
- Shoulder joint medial rotation and elbow flexion
- Shoulder joint adduction and downward scapular motion
- Inertial round-off and release (partial supination and shoulder joint lateral rotation).
Silvia also advocated the drag theory of swimming propulsion, and that theory has been debated in recent years, but his kinesiological analysis of the mechanics of Rose's stroke has not been successfully challenged.
What are the stroke characteristics that the current Australian star freestylers show that may be lacking in many of their competitors?
Number one is their form, which essentially follows the description of Silvia's "Big Four." Most notable is the catch at the beginning of the propulsive phase of their strokes. Silvia would have described this as an inertial positioning movement before the main propulsive phase begins.
At this point in the stroke, it is obvious that the great Australian freestylers tale the time to assume the high elbow position about which all good coaches talk. They accomplish this act by internally (medially) rotating the upper arm bone (humerus) and flexing the elbow. This action ends with the forearm and hand assuming an almost perpendicular position in relation to the surface of the water, before the elbow is moved (adducted) toward the feet. The positioning movement of the arm takes place in the shoulder with very little muscular force.
It is after the catch that the true power and efficiency of the Australian crawl stroke technique is exhibited. It is during this most propulsive phase that the Australians use the power of the shoulder joint most effectively by adducting the upper arm bone (humerus) along the frontal plane (the plane that divides the front of the body from the back) of the body.
This is the same movement a gymnast would use in performing the iron cross on the still rings. The only difference between the gymnastic and swimming actions is in the flexion of the swimmer's elbows to increase the mechanical advantage of the arm's lever system. This position also fits beautifully the position needed to apply force backward with the hand and forearm that is required in the drag theory of propulsion.
The swimmer's muscular action, also, is not static. The elbow is brought vigorously toward the body (adduction). It is the great prime movers of Numeral adduction, the teres major, latissimus dorsi and the pectoralis major that perform the bulk of the task. These muscles are most effective when their angles of pull follow closely along the frontal plane of the body. This most powerful movement of the shoulder joint is demonstrated skillfully in the crawl stroke swimming of the current flock of Australian male world-class swimmers.
It also stands to reason that the most powerful movement of the shoulder-adduction of the upper arm bone (humerus) along the frontal plane of the body (the plane that divides the body from front to back)-is the so-called "swimming with the trunk of the body, or core" that is now being promoted by many coaches. This is because it is the great muscles of the trunk that perform the bulk of the task.
The long, propulsive phase of the great Australian swimmers is finished with the completion of adduction, and the recovery is initiated by rounding off the stroke and partially supinating the hand (turning the palm toward the body).
The supination of the hand effectively releases the swimmer's feel for the water as the swimmer redirects the momentum of vigorous adduction into an inertial recovery. The elbows of the Australians remain bent as they finish their strokes so that the mechanical advantage of the shortened lever arm can be maintained.
The bent elbow finish is important because the intuitive swimmer knows that the advantage of pushing past the hip by extending the elbow does not contribute to an inertial, free swinging and non-muscular recovery. This recovery is a bit different from the butterfly.
The butterfly recovery cannot rely on trunk rotation. And the more lateral recovery in the butterfly requires a straight elbow to prevent excessive lifting of the shoulders to clear the water at the beginning of the recovery. The rotation of the trunk on its long axis as adduction is completed adds to the disadvantage of extending the elbows in the crawl stroke as the hand effectively loses its propulsive grip on the water at the completion of adduction.
It is important to note that the "core or trunk" swimming of the great Australian freestylers emphasizes the motions of the largest and most powerful muscles of the trunk while minimizing the involvement of the smaller muscles of the arm and forearm. It is in describing these actions that the importance of correct language becomes apparent.
The action of adduction along the frontal plane of the body will cause the arm to be moved in a curvilinear arc (the arm being a lever system with the fulcrum at the shoulder end). It is not necessary for a swimmer to try to stroke in "S" patterns or to think to move in downsweeps, outsweeps, insweeps and upsweeps.
Emphasis of these sweeping actions could easily confuse the swimmer into making motions not congruent with the true power of the shoulder joint. One of the major problems of describing technique with sweeps and "S's" is that they describe actions that can be interpreted in many different ways. An "S" sweep done in front of the body is much different from an "S" sweep beside the body.
And, any exaggeration of sweeping actions would naturally deviate from the power of adduction and the strength inherent in the great trunk muscles. In addition, the resulting actions would greatly increase the involvement of the smaller muscles of the arm and forearm, resulting in early fatigue. It was stated earlier that Silvia's kinesiological descriptions of technique have not been successfully refuted. It was his reasoning that this technique fits the drag theory of force that has been in question. Ever since Doc Counsilman first professed lift as the major force of swimming propulsion in the early '70s, and others have promoted it such as Ernie Maglischo in his widely circulated books, "Swimming Faster" and "Swimming Even Faster" in the '80s and '90s, Silvia's ideas have collected dust. It was unfortunate that Silvia's descriptions were mostly ignored because they were so accurate, even if his theory of propulsion was considered antiquated.
Counsilman's lift theory promoted the use of curvilinear motions to produce propulsion. In the lift model, the hand formed an airplane-type wing that, when moved sideways to the direction of travel, created lift.
Silvia's drag model of propulsion followed Newton's Third Law, "for every action there is an equal and opposite reaction." The mounting evidence in research supports Silvia's ideas on propulsion.
Springings and Koehler in their article, "The choice between Bernoulli's or Newton's model in predicting dynamic lift," lay bare the arguments supporting lift as the primary or even a significant force in swimming. Maglischo is now reconsidering lift theory and is revisiting Silvia's ideas, but if technique is as important as most world-class coaches believe, the promotion of a flawed theory for an extended time by influential thinkers, coaches and authors would be an obvious detriment to swimming progress.
Unfortunately, the use of inaccurate and misleading descriptions of crawl stroke technique, including "S" curves and sweeping actions, is exactly what the lift theorists have promoted in this country for over 20 years. These descriptions remain even as the theory of lift is refuted.
It is the contention of this writer that one of the main reasons the Australians are now so superior to the rest of the world in the male freestyle events from 200 to 1500 meters is that their technique follows a mechanically superior model. Theories of propulsion used in Australia take a back seat to what produces results. While the model for technique in the United States and elsewhere has been promoting actions that are not congruent with the strength of the shoulder joint, the Australian model does the exact opposite.
It could be argued that the United States has been competitive in the sprint freestyle events even up to the 400 meters in recent years. Thus, the argument in the previous paragraph would be flawed.
However, the quick nature of sprinting events demand intuitive swimmers who naturally avoid the time wasting and excessively inefficient curvilinear motions being promoted.
The vast American talent pool has been able, thus far, to find and develop successful sprinters. The Australians have a talent pool seven percent of the United States and have produced world records starting with Kieren Perkins in the 1500 and ending with the most recent world records of Ian Thorpe.
It is now not a stretch to think that the Australians could add the 50 and 100 meter world records if the proper athlete could be found to match their superior technique.
Perhaps with maturity that athlete could be Ian Thorpe. He certainly has shown the speed to be competitive with his 48.55 split in the 4 x 100 relay at the Pan Pac Championships in 1999. In the meantime, the United States, which has been competitive in most freestyle events, now finds itself with competitors who are significantly slower than the Australians in a number of freestyle events.
It is interesting to note that it not just the likes of worldclass performers such as Ian Thorpe, Grant Hackett and Kieren Perkins who are currently exhibiting this peculiar technique in Australia. Dick Hannula attended a training session of Ian Thorpe and Grant Hackett in May 1999 while he was visiting Australia to speak at the Australian Swimming Coaches and Teachers Association Convention. A local swim club was practicing at the same time as the national team members, and he noted that the age groupers were using the same basic technique.
Hannula states in his observations of their freestylers that there were no sideward sweeps. He also notes that this technique is not what is described in textbooks. Whether or not Australian coaches understand kinesiological principles, the Australians obviously follow a superior stroke model that is promoted at the earliest levels of competition.
Hannula goes on to state that, while this technique appears to be a new innovation, he has seen it as far as 15 years or more ago in sprinters such as former American record holder Robin Leamy. As stated earlier, this stroke technique can be seen as far back as Murray Rose in the 1950s. And, since Rose was a distance freestyler, it is a stroke that has been used by freestylers at every distance. Other hypotheses have been presented over recent years concerning the lack of progress of the male distance freestyle events in the United States. The hypotheses include both cultural and coaching issues. The cultural hypothesis states that there are fewer and fewer athletes in the Untied States willing to do the work required for success in the distance events.
Our fast-paced society, with its emphasis on instant gratification, might be discouraging talented athletes from pursuing distance events. Also, there is more competition from other sports and activities outside sport. All these distractions add up to a negative result at the top of the performance ladder.
The coaching hypothesis points to the disproportionate number of swimming programs that emphasize sprinting because the overwhelming majority of swimming events are sprints.
While both of these arguments are worthy of consideration, I do not believe the key answer lies in their conclusions. These arguments needlessly berate and belittle the hard work and dedication of the current national and worldclass stars of American distance swimming. All world-class swimmers, regardless of their event, know there are no short cuts to success. And the American successes in other swimming events show the dedication and depth of swimming in the United States. And, once a swimmer sees the possibilities of international competition, the motivation to do what it takes to succeed is universal.
Ian Thorpe's Stroke
Brent Rushall on his internet page describes in detail the stroke of Ian Thorpe as he set the world record in the 400 meter freestyle last summer at the Pan Pac Championships. The frame-by-frame analysis shows the champion's stroke that, again, fits the description of a stroke Silvia would have promoted, or anyone else for that matter. It is in the understanding of what they see that theorists differ.
Again, the general mechanical description Silvia used with his "Big Four" essentially could be used as a description of Thorpe's stroke. Rushall notes in his analysis a few peculiarities in Thorpe's stroke that are not included in Silvia's "Big Four." While not essential to nor negating the premise of the "Big Four," these peculiarities are significant enough to warrant a discussion of their nature.
Rushall notes the apparent catch-up nature of Thorpe's stroke. This is described as the duration of the recovery (four-tenths of a second) and the duration of the pull (one second for the right hand and 1.1 seconds for the left hand).
This imbalance between recovery and propulsive phases (0.4 sec./1.0 sec. and 0.4 sec./1.1 sec.) can be explained through a discussion of the forces involved. The recovery naturally will take less time as it takes place over water, inertially and with little resistance.
Thorpe does not rush the initial part of the propulsive phase of his stroke, as he takes the time to position the hand and forearm by medially rotating the humerus and flexing the elbow. It is once this position is attained that the prime movers of adduction vigorously contract against the resistance of the water.
Adduction continues until the elbow almost touches the body. At this point, round-off, partial supination of the hand and the release take place. These actions against the resistance of the water naturally take more time than the recovery. Any effort on the part of the swimmer to slow the recovery to maintain opposition will negate the advantage of an inertial and non-muscular recovery.
At this point in the discussion, it could be argued that Thorpe's stroke could be improved by maintaining the bent elbow of the recovery to decrease the inertial lag time taken as the arm is stretched out straight during the entry phase of the stroke.
However, this action would not allow for full inertial shoulder girdle elevation described in Silvia's "Big Four," and would negate the ending of the propulsive phase of the opposing arm. The resulting stroke would be shortened and less effective during the initial propulsive phase.
Clearly, Thorpe does not rush his stroke, and he takes the time to complete each phase. There is no inefficient hurryup, or "spinning of wheels," that is often exhibited by less talented swimmers.
Thorpe's apparent lack of speed in assuming the medial rotated position with elbow flexion is the result of the inertial completion of the recovery phase. Very little muscular force is used to gain this position. The speed of the hand and the arm when the hand and arm were recovering out of the water has slowed with the added resistance of the water.
Rushall describes two 17-frame clips of Thorpe during his 400 meter world record at the Pan Pacs in 1999. One clip is taken at 75 meters into the swim and the other clip is taken at 375 meters into the swim. Each frame is one-tenth of a second apart and makes the total sequence of each clip 1.7 seconds long. It appears that the final two frames of each clip are a repeat of the first two frames. This would make the stroke cycle 1.5 seconds long in each clip.
The first five frames of the sequence taken at the 375 meter mark of the race show the right arm with the elbow completely extended. Not until the sixth frame does any elbow flexion become apparent. This would suggest that one-half of the in-water phase of the stroke cycle of Ian Thorpe is non-propulsive and that little or no pushing down or out takes place during this phase of the stroke.
Any increase in the muscular force to produce this positioning movement would be detrimental to the stroke.
The efficiency of Thorpe's stroke lies in his ability to get into the medial rotated position with elbow flexion while the arm is still fully abducted and the shoulder girdle is elevated (the position an eager child uses when he raises his hand to answer a teacher's question) and before the am begins its forceful adduction movement.
This manifests itself as a position that allows the hand and forearm to gain almost a perpendicular position in relation to the surface of the water before the elbow passes the top of the head during adduction.
The fact that Thorpe takes five-tenths of a second to accomplish this movement in a 1.5-second total stroke cycle demonstrates the importance of this positioning movement to the stroke.
Clearly, Thorpe takes the time to achieve the medial rotated position, and he does it inertially and with little antagonistic muscular interference. Any increased muscular force used to speed up this positioning movement would not add significantly to propulsion and would involve the internal rotator muscles of the rotator cuff and the large adductors that are also involved with the main propulsive phase of the stroke which follows.
The advantage of the inertial positioning movement of medial rotation instead of a vigorous muscular action involves the size, nature and positioning of the muscles involved. The rotator cuff muscles are relatively small muscles whose main purpose is to serve as tendons to hold the head of the arm bone (humerus) into place in the shoulder joint.
Any emphasis upon these muscles to provide more than stabilization of the shoulder would invite early fatigue. Vigorous contractions of the other internal rotators which are also major adductors of the humerus, the latissimus dorsi, pectoralis major and the teres major, would be an ineffective recruitment of muscles at an ineffective angle of pull.
Certainly, the inertial positioning of internal rotation is promoted by an effective kick that allows the entry hand to be positioned as the body continues to provide propulsion with the kick. This is demonstrated by Thorpe and illustrated with the sensation a swimmer gets when swimming with flippers.
The flippered swimmer has the sensation that the arm stroke is too easy, especially during the early positioning phase of the stroke. It is my opinion that this is what Ian Thorpe must feel as he swims. And, knowing the size (17) and flexibility exhibited in Thorpe's feet, the advantage of superior body structure only adds to an already efficient technique. The inertial and non-muscular nature of twothirds of Ian Thorpe's stroke (the recovery and catch phases) adds to the endurance of the swimmer.
All good swimmers make it look easy, and in this case, it most certainly, there is no one who has exhibited the standpoint of efficiency.
Surely, there is no one who has exhibited the current superiority of Australian male freestylers. There is not just one freak individual performing outstanding feats. There is a whole group of Australian male swimmers who, together, form a very formidable team. The current Australian stars emulate a technique that is best described by the drag theorists and follows the kinesiological model of what is humanly mechanically superior. The current Australian superiority in the freestyle events is a result of the outstanding application of an old technique applied by superior athletes who are well-trained and highly motivated.
I believe that it is the technique of the Australians that is the greatest factor in separating the Australians from the rest of the world-class swimmers. And no amount of training, outstanding body type or determination on the part of the athlete will make up for the lack of the application of this technique.
Position du coude en images
Epaule avancée et fixée, coude haut, poussée de la main et de l'avant-bras: Natalie Coughlin en action:
Total Immersion Strategies - A Closer Look
In their book Total Immersion, Terry Laughlin and John Delves express ideas related to swimming more efficiently in an entertaining and effective manner. Chapter 2 in particular - entitled Swim Better Without Getting Any Stronger? Yes! - has great appeal. Additional insight can be gained by considering factors, from a biomechanical perspective, that might contribute to the success of the strategies applied in the Total Immersion program.
It was pleasing that the authors recognised the interaction effects of stroke length and stroke frequency. It is an indisputable fact that speed (V) is the product of stroke length and stroke frequency (V = SL * SR). However, there has been a tendency in the past not to recognise the fact that changing stroke frequency changes stroke length and that changing stroke length changes stroke frequency. That is, they are not independent of each other. Therefore, as the authors have indicated, increasing either stroke length or stroke frequency does not necessarily mean that speed will increase. In fact, it might reduce velocity.
It is natural to think that increasing stroke rate will increase speed. Actually, this is only the case if the increased rate results in a greater propulsive impulse (average propulsive force * time the forces act) over the period of a stroke cycle without an equivalent increase in resistive impulse (average resistive force * time over which the forces act) encountered at the original speed. When propulsive impulse is increased more than resistive impulse a swimmer's speed will increase until the resistive impulse and propulsive impulse are equal over the period of a stroke cycle. This equality occurs naturally due to increasing resistance with increasing speed.
Because speed depends on the interplay of propulsive and resistive impulses we need to think of swimming in terms of propulsive and resistive impulses rather than in terms of stroke length and stroke rate. Stroke length, stroke rate and speed are all outcomes of the swimmer's efforts to produce propulsive impulse and to reduce resistive impulse. We should think of stroke length, stroke rate, and speed as outcomes of the propulsive and resistive impulses. For this reason, an 'impulse' model rather than the traditional 'stroke length/stroke rate' model is appropriate.
Notice that impulse depends on the magnitude of the forces applied and the time over which they act. Then what options does the swimmer have to increase speed? Basically, there are four options, or an effective combination of those four options. They are:
- Increase the magnitude of the propulsive forces
- Increase the time of the propulsive forces
- Reduce the magnitude of the resistive forces
- Reduce the time of the resistive forces
A Strategy: Increase the Magnitude of the Propulsive Force and Reduce the Time of the Resistive Force. Would this work?
A swimmer's natural instinct is to increase the magnitude of propulsive force and to reduce the cycle time so that the time of resistive force is reduced. Thus, the swimmer pulls harder and faster under the water and also recovers the arm faster. The time between entry and the start of the downward and backward movement of the hand is also reduced. With the reduced cycle time the swimmer naturally kicks at an increased rate. However, let's neglect the effect of kicking on propulsion and resistance for the present and focus on the propulsion produced by the arm pull.
The 'fast arms' strategy for increasing speed seems totally logical because the magnitude of propulsive force is increased, and the cycle time is reduced thereby reducing the resistive impulse. This strategy should be effective in increasing speed provided that:
- The reduction in time of the pull that occurs because the hand is pulled quickly through the water, is more than offset by the increase in magnitude of the propulsive force.
- The magnitude of the resistive force does not increase.
We could expect that the faster pull would yield a greater propulsive impulse despite the reduction in time of force application because force is proportional to the square of speed of the hand given by the formula:
Fh = ½CAdV2
Where: Fh is the force produced by the hand, C is the coefficient of fluid resistance at a given hand orientation to the flow, A is the cross sectional area of the hand with respect to the direction of flow, d is the density of the fluid, and V is the speed of the hand.
However, the magnitude of the force will only compensate for the reduction in time of the pull to yield a greater propulsive impulse if:
- The hand is oriented at appropriate angles so that the coefficient C and cross sectional area A are maximised and the forces produced are predominantly in the desired direction of travel.
- The forces are sustained at a high level by having fast movement throughout the time of the pull.
Assuming that those conditions are met then the strategy of increasing speed by increasing propulsive impulse and reducing the time of resistive impulse might work.
However, the question of whether the magnitude of the propulsive force and the fast cycle rate can be sustained must now be addressed. Given that the magnitude of forces applied during the pull is large, the speed of muscle contraction is great, and the stroke cycle time is short, then the rate of doing physiological work is increased. The increased work rate means that the increased speed is attained only with increased effort and cannot be sustained. However, this does not necessarily mean that the swimmer will revert to a slower stroke rate. The swimmer is still trying to go fast and is still trying to apply the strategy of maintaining a high stroke rate! However, in order to maintain the stroke rate several things happen that prevent the provisos above being met:
When one is trying to maintain a fast cycle time while reducing the effort, it is likely that one or more of several changes to the stroke pattern will occur:
- The hand will be oriented so that its cross-sectional area to the flow and its coefficient of fluid resistance are reduced. That is, the hand 'slips' through the water more easily. While this allows the speed of the hand movement to be sustained, the force produced is reduced and the propulsive impulse is reduced as a consequence. This could occur near the start of the stroke, near exit, and even throughout the mid portion of the stroke.
- To maintain a fast cycle rate the stroke may be 'shortened'. It is likely that the swimmer will not reach the hand as far forward and will let the hand 'drop' prior to making the catch. The swimmer may also release the water earlier during the exit phase. Therefore, while the below-water phase of the arm action may be the same duration as previously, the time during which propulsive forces are produced has decreased.
- The swimmer may use a more 'direct' path of the hand. For any given speed of hand movement the quickest path is a straight line. The formula provided above indicates that the force produced is related to the square of the speed of the hand with respect to the flow. Given a fixed amount of time to cover a distance, a straight-line path requires less hand speed than a curved path. Therefore, less propulsive force is produced when a straight-line path is used. Further, a straight-line path causes the water to move with the hand and the actual speed of flow around the hand is less than when the hand is finding 'still water'. Further still, recent evidence suggests that good swimmers incorporate direction changes in the path to make use of additional propulsive forces that can be generated from production and shedding of vortices. This means that a swimmer who adopts a straight-line path to maintain a fast stroke rate may be reducing propulsive forces in all of those three ways.
The assumption that resistive forces do not increase with an increase in stroke rate also needs to be considered. As we will see when we delve deeply into why the strategies used in the Total Immersion program are effective, it is likely that there is, in fact, an increase in the magnitude of resistive forces when stroke rate is increased.
However, at this stage, based on the foregoing discussion above, we can readily identify adverse effects on resistance in the case of a swimmer who is struggling to maintain a fast stroke rate. Such a swimmer is likely to 'shorten' the stroke. In that case the hand and arm are likely to enter steeply, encountering increases in resistive force, and if the arm 'drops' from an extended and streamlined position before making the catch, resistive forces are also increased. Increases in resistive force arising from less than optimal alignment and streamlining are also associated with an increased stroke rate. These will be discussed further as we look at why the strategies described by the authors are effective.
OK. What's Another Strategy?
The strategies used in the Total Immersion program are based on the idea that a swimmer can improve in speed without an increase in effort. It advocates a reduction in stroke rate rather than an increase. This is counter-intuitive! It means that the stroke cycle is longer and therefore the swimmer is subject to resistive forces for a longer period. Thus, to increase speed despite an increase in cycle time, there are several options:
- Increase propulsive forces.
- Increase the time of propulsive forces.
- Reduce resistive forces.
Change in stroke length is one of the outcomes of changing the cycle time. For a given speed sustained across many cycles, increasing cycle time must mean an increase in stroke length. However, for that speed to be maintained, propulsive impulse must be equivalent to resistive impulse. Let's say that the average resistive force over a cycle remains the same. Then increasing the cycle time means that the resistive impulse is increased. To match that impulse with an equivalent propulsive impulse the swimmer must increase the magnitude of propulsive force or apply propulsive forces for a longer period. Both of those options mean that an increased effort is required.
As stated by Terry Laughlin and John Delves, the key to improving speed without an increase in effort is to reduce resistive forces. Reducing resistive forces allows the same speed to be attained as previously but with a decreased stroke rate. That is, the same resistive impulse would be achieved by offsetting a reduced force with a longer time. Provided that the resistive impulse remains matched by an equivalent propulsive impulse, then the same speed is achieved with a decreased stroke rate. A slower stroke rate naturally leads to a longer stroke length in keeping with the immutable relationship V= SR * SL.
Terry Laughlin and John Delves indicate that reducing resistance and increasing stroke lengths go 'hand in hand'. Certainly, good swimmers are characterised by long stroke lengths. However, it may be preferable to think in terms of reducing resistance as a goal rather than increasing stroke length. When resistance is reduced, longer stroke lengths follow naturally in accordance with the laws of motion. The implication for the swimmer is to think in terms of reducing resistance rather than in terms of increasing stroke length. If resistive forces are reduced then, at any given speed, the stroke length must increase as an automatic consequence.
In the above scenario we have assumed that the speed is kept the same, the resistive impulse during the stroke cycle is kept the same and, therefore, the propulsive impulse during the stroke cycle is kept the same. If the resistive impulse is the same then when the magnitude of resistive forces was reduced the cycle time increased. We changed the relative effect of the magnitude of the force and the time over which it acts on total resistive impulse. We can now think about similar scenarios with propulsive impulse. That is, we could look at the relative magnitudes of propulsive force and time over which it acts when the cycle time is lengthened due to reduced resistive forces as described above.
In fact, changing the resistive force does not demand a change in the way propulsive force is produced. The pull could be executed in the same way, thereby generating the same propulsive impulse. If the hand and arm are moved at the same speeds through the same distance and in the same time then the propulsive impulse remains unchanged. However, because the cycle time is now increased due to the reduction in resistive forces described above, there remains a longer time for the recovery phase. The net result is that the effort below the water could be the same as previously, but there is now a longer rest period for the muscles that were used during the pull. This means that the work done over the period of a whole cycle is done over a longer period. That is, the physiological demands are less and swimming at that given speed is less effort than prior to the changes that reduced resistive forces.
In addition to the longer rest period, there are likely to be other advantages resulting from the increased cycle time. First, the swimmer can take the time to extend the recovering arm fully following entry. This means that there is potential to pull over a greater distance, thereby generating a larger propulsive impulse. Second, the pull can commence with the arm in a streamlined position and then the catch to be made early in the pull. This not only lengthens the period of the pull but reduces the resistance prior to the catch. Recall that the tendency for swimmers who are trying to maintain a fast stroke rate is to not reach the hand forward sufficiently to a streamlined position. Rather they tend to enter steeply and to 'drop' the arm to a position that causes increased resistance prior to making the catch. The distance then remaining to generate propulsive impulse is shorter than when the swimmer has had the time to extend fully. The swimmer also has time to push the hand backwards, to fully utilise the range of motion to apply forces, and to make a clean exit rather than having to 'release' the water prematurely in order to maintain a fast stroke rate. Rushing in this manner cuts the propulsive phase short and increases resistance during exit.
So, all that has to be done to reduce the effort required to maintain a certain speed, or alternatively, to increase the speed for a given effort, is to reduce resistance. In doing so, there will be, as a natural consequence, an increase in stroke length and a reduction in stroke rate at any given speed. Sounds simple and obvious. However, reducing resistance may be more easily said than done!
How Do I Reduce My Resistance?
The Total Immersion program uses several 'tricks' that reduce resistance. Three phrases summarise the goals in terms of body postures and actions that can be visualised by the swimmer:
- Balance your body better in the water.
- Make your body longer.
- Swim on your side.
At first glance these seem very strange. Of course, the wording should not be taken at face value. The authors are intending that the swimmer thinks conceptually rather than literally.
Balancing the Rotational Torques
With respect to balance in the water the main concern is the problem of 'sinking legs'. In a prone float position, the centre of gravity is further from the head and closer to the feet than the centre of buoyancy in most swimmers. This is because the chest is less dense than the legs. As a consequence of the centre of mass and centre of buoyancy being out of alignment, the body tends to rotate so that the legs 'sink'. When swimming, a sloping body and legs increases resistance. This can be partially overcome by kicking. Kicking produces a counter torque to balance the body and allow it to travel in a more level position. However, there is obviously a physiological cost of kicking.
Terry Laughlin and John Delves propose that 'pressing your buoy', i.e. the chest area, downwards can assist in gaining a level alignment. However, while this is an image that swimmers might be able to use, the mechanical reality is that the balancing effect must come from external torques. Thus, the 'buoy' might be 'pushed down' by generating external torques somehow. Without generating the external torques by some mechanism, 'pressing your buoy' is akin to 'lifting oneself by one's shoe laces'.
Therefore, we need to look for mechanisms by which the balance can be obtained. Kicking is one way. In the absence of kicking, the body will reach an equilibrium position at a particular body angle and speed using torques generated by the force of water pushing against the angled body. The force tends to lift the legs. However, when a body is moving through the water at an angle there is considerable resistance to forward motion.
These video clips illustrate the alignment of a swimmer with and without the aid of kicking. Clearly, when there is no kicking, the body's rotational equilibrium is attained at a much greater angle and the swimmer's motion is greatly affected by resistive drag.
Other Balancing Torques
What other torques can be used to attain horizontal alignment? Terry Laughlin and John Delves describe a 'catch up' technique that makes the body 'longer'. In essence, the 'catch up' technique means that the recovering arm is about to enter the water when the pulling arm starts its pull. This is achieved by delaying the start of the pull after entry. The hand reaches forward and then the arm and body are maintained in a streamlined glide while the recovering arm moves forward. Thus, the body is effectively 'longer for longer'.
| I'm not long for long: |
I'm longer for longer: |
Terry Laughlin and John Delves indicate that this helps to make the body 'longer' and thereby reduces drag in accordance with the Froude principles applied to floating vessels. This idea has some appeal. Certainly there is evidence that longer swimmers have advantages with respect to drag reduction in addition to the advantages of having longer limbs to propel the body. Whether using a 'catch up' reduces drag by making the 'vessel' longer and thereby reducing wave drag in accord with the Froude relationships requires more research. It may be that the human body is too irregular in shape to gain an advantage in the same manner as vessels of streamlined shape.
However, it may be that reduced drag associated with a 'catch up' technique is related more to reducing form drag than to reducing wave drag by having a longer body. In particular, the 'catch up' means that there is more mass forward of the lungs, and for a longer period, than in a technique with high stroke rate used by unskilled swimmers. Consequently, the centre of mass and centre of buoyancy are more closely aligned, thereby reducing the turning effect tending to 'sink' the legs.
In the video clips above, the swimmer on the left is showing the effect on balance when the submerged arm is in a backward position while the swimmer on the right is indicating the effect on balance when the submerged arm is in a forward position. In both cases, the arm above the water is simulating the position of mid-recovery. Notice that the swimmer on the left 'sinks' because the centre of gravity is behind the centre of buoyancy.
Thus, by pausing after entry with the arm in a streamlined position so that the other arm almost 'catches up' we have the desirable situation whereby the resistance is reduced, stroke rate is reduced, speed is maintained, and as a consequence, stroke length is increased. Further, the rate of energy expenditure is reduced because:
- The need for kicking to maintain horizontal alignment is reduced.
- The effort supplied by the pulling arm is applied with reduced rate due to the longer cycle time.
The video clips above show a swimmer using a 'catch up' stroke and a stroke with higher stroke rate. There was no kicking in either case. Notice that the alignment of the swimmer using the 'catch up' stroke was more horizontal than the swimmer using the stroke with the higher stroke rate.
The video clips above show a swimmer using a 'catch up' stroke and a stroke with higher stroke rate. In this case a kick was used to maintain horizontal alignment. Notice that the swimmer using the 'catch up' stroke maintains horizontal alignment with a less vigorous kick than the swimmer using the stroke with the higher stroke rate.
Another torque that tends to 'sink' the legs is the torque produced by the upward force in reaction to the downward movement of the arm and hand at entry and following entry. When one is attempting to cycle the arms quickly, the hand and arm tend to be driven downwards during and after entry rather than stretching forward and holding a level position prior to the pull as in the case of the 'catch up' technique. When the pull commences in the 'catch up' technique, the forces can be generated so that the upward component tending to produce unwanted 'sinking' rotation is relatively small. That is, the swimmer is focusing on pulling backwards rather than pushing downwards. Further, at this time, the recovering arm is well forward and is above the water, thereby producing a strong torque countering the 'sinking' torques. This may contribute to the swimmer's feeling of 'pressing the buoy'.
Body Roll and Resistance
Terry Laughlin and John Delves provide a very effective analogy for reducing resistance by being more on one's side. In this analogy they compare the resistance of a flat barge with that of a leaning yacht. The leaning yacht cuts the surface with a narrower profile and thereby produces less wave and form drag. Certainly, unskilled swimmers tend to be either 'rolling and wobbling all over the place' and thereby are in un-streamlined positions that do not facilitate smooth flow over the body, or they are swimming with inadequate body roll. A range of body roll whereby the cross sectional area cutting through the water at its surface is less than when the body is flat is certainly desirable in reducing wave drag and form drag. When the swimmer has one arm stretched forward, rotation to about 45 degrees about the long axis facilitates a streamlined position to glide through the water. In this position the water can flow readily along the body with little disruption around the submerged shoulder. Further, the body roll allows the arm to be merged nicely with the head. Meanwhile, the shoulder of the recovering arm presents an abrupt and irregular path for flowing water. However, the body roll has assisted in getting the recovering shoulder clear of the water so that the effect of the irregular shape on flow is minimised.
When the stroke rate is fast, the roll associated with the pull is well under way during the recovery of the non-pulling arm. Therefore, it is not possible to have the resistance-reducing posture described above. Further, when swimming with a fast stroke rate it is difficult to roll through a large angle. One reason is that there is a lack of time. Also, attempting to have a large body roll in a short period of time makes if difficult to maintain smooth flow over the body. The rapid changes in posture as the water flows around it tend to produce turbulence and therefore increased drag.
Observe the videos above frame by frame and observe how the 'catch up' technique (on the left) allows good body roll to facilitate smooth flow of water around the body while the body roll used in the technique with a fast stroke rate (on the right) does not facilitate as smooth a flow.
Other Advantages of Body Roll
Body roll also puts the body in a strong position to apply forces. A well-timed body roll can do much of the work in pulling the hand through the water, thereby using the large muscles efficiently and reducing the load on more easily fatigued small muscles. As the timing moves towards the 'catch up' technique the forward stretch and attainment of the glide position is facilitated by the body roll, the roll helps to make a strong catch and initiate the pull and then to continue the pull through to exit. By that time, the body is well on its side and exit is easy. Conversely, when a faster stroke rate is used, the amount of roll tends to be limited by the time available. The body is preparing to roll in the opposite direction as the pull of the opposite hand is commencing. Therefore, exit is made more difficult.
The photos above show the instant of exit in swimming without a 'catch up' (left) and the instant of exit in swimming with a 'catch up'. Notice that the swimmer using a 'catch up' has greater body roll than the swimmer without a 'catch up'.
Summary
The ideas expressed by Terry Laughlin and John Delves in their chapter 'Swim Better Without Getting any Stronger?Yes!' were discussed with reference to a mechanical model featuring resistive and propulsive impulse. In agreement with the authors, reduction of resistive force was viewed as the key to improving swimming technique. Reducing resistance enables a slower stroke rate at any given speed and a reduced rate of energy expenditure. Increased stroke length is a natural consequence of the reduced stroke rate.
The question of how resistance can be reduced was then addressed. While consideration of a mechanical model led to explanations that differed in some ways from the explanations proposed by Terry Laughlin and John Delves, there was agreement that changing the stroke to a 'catch up' technique, by maintaining a streamlined reach of the arm and hand after entry, could reduce resistance. In this article it was proposed that the 'catch-up' technique reduced resistance by two main mechanisms:
- It reduces the torques that tend to 'sink the legs' by moving the centre of mass forward so that it coincided more closely with the centre of buoyancy.
- It encourages appropriate range and timing of body roll. Thus, the swimmer can readily adopt positions that minimise resistance during some phases of the stroke, particularly during exit and recovery.
Le "Catch"
Le "catch" est le terme anglosaxon qui sert à désigner l'accroche sur l'eau: juste avant la phase propulsive, la main et l'avant-bras "attrape" l'eau. Plus la surface qui accroche l'eau est importante, plus la puissance de la propulsion sera grande. Il faut donc chercher à appuyer sur l'eau avec la main perpendiculaire au mouvement (c'est à dire que la paume fait face au mur du bassin derrière le nageur) et également avec l'avant bras.
Pour permettre cette accroche avec l'avant-bras, il faut casser le coude sans bouger l'épaule. La fixation de l'épaule est déterminante. Si l'épaule est fuyante, il est très difficile d'avoir un cassé du coude efficace. En outre, une fois le catch réalisé, c'est la force de levier du bras qui va jouer: pour que cette force s'exerce au mieux, il faut que l'axe du levier (cad l'épaule) soit le plus fixe possible. Sinon la force de levier perd en force.
Il faut donc "bloquer" l'épaule lors de la phase du catch et le début de la phase propulsive.
Quitte à bloquer l'épaule, autant la bloquer en avant près du visage: cela permet un catch très rapide et également un plus grand hydrodynanisme car si l'épaule est loin du visage, la surface frontale qu'offre le nageur à l'eau est plus importante. Au contraire, en ayant l'épaule qui touche la joue, on réduit considérablement la surface frontale qui s'oppose à l'eau.
Un excellent exemple de "catch" épaule avancée et fixée est celui de Laure Manaudou (voir photo sur le site).
Les anglosaxons utilisent l'expression "Swim Over the Barrel" (littéralement "nager au dessus d'un tonneau") pour illustrer le "catch" qui consiste à avoir l'épaule avancé, le coude cassé, et le bras qui forme une sorte d'arc de cercle un peu comme si vous cherchiez à glisser votre main le long d'un tonneau serait juste sous vous lorsque vous nagez dans un sens perpendiculaire à l'avancement. En plus la forme "arc de cercle" reprend un peu la forme d'une aile d'avion avec l'effet porteur qui en découle et qui donc pousse le nageur vers l'avant : l'eau sur le devant du bras a un trajet plus long à faire que l'eau derrière le bras: il y a donc comme pour une aile d'avion un effet de portée qui s'applique derrière le bras.