Biomechanics and Medicine in Swimming XI

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Synchronized underwater video and hand force data shows swimmers and coaches exactly where in the stroke cycle that wasted motion and force losses occur. For example, the swimmer in the left image of Figure 4 shows .2 sec of wasted motion at the beginning of the butterfly pull and the swimmer in the right image shows a major force loss as the arms pass under the shoulders. Armed with this information, the coach can suggest technique adjustments to minimize these limiting factors. When a quantitative analysis is not feasible, coaches can qualitatively evaluate swimmers to identify wasted motion (as shown by excess lateral hand motion) and force losses (as shown by sudden changes in hand path). Coaches can then target control of the hand path angle to help a swimmer overcome these limitations. A quantitative analysis, however, is the most definitive way to identify limitations, confirm the effect of technique adjustments, provide numerical feedback to swimmers, and ensure that swimmers make the precise changes to optimize performance. Figure 4. Captured screens of Aquanex+Video images showing butterfly swimmers with wasted motion (top) and a major force loss (bottom). In each screen, the vertical lines on the force curves are synchronized with the video image. chaPter5.education,adviceandBiofeedBack conclusIons Coaches can help slower swimmers improve by emphasizing technique instruction and regularly measuring their C d . Because of the large gains in v that result from small decreases in C d , even the fastest swimmers can continue to benefit from improving technique. Faster swimmers can also gain a greater advantage over slower swimmers from a more effective use of strength. With a detailed hand force analysis, a coach can identify wasted motion and force losses to provide options that increase average force and achieve maximum performance potential. reFerences Becker, T.J., & Havriluk, R. (2010). Quantitative Data Supplements Qualitative Evaluations of Butterfly Swimming. In Kjendlie P.L., Stallman R.K. and Cabri J. (eds): Biomechanics and Medicine in Swimming XI (in press). Havriluk, R. (2003). Performance level differences in swimming drag coefficient. Paper presented at the VIIth IOC Olympic World Congress on Sport Sciences, Athens. Havriluk, R. (2004). Hand force and swimming velocity. Paper presented at the XVth FINA World Sports Medicine Congress, Indianapolis, IN. Havriluk, R. (2006a). Analyzing hand force in swimming: Three typical limiting factors. American Swimming Magazine, 2006(3), 14-18. Havriluk, R. (2006b). Magnitude of the effect of an instructional intervention on swimming technique and performance. In J. P. Vilas-Boas, F. Alves, A. Marques (Eds.), Biomechanics and Medicine in Swimming X. Portuguese Journal of Sport Sciences, 6(Suppl. 2), 218-220. Havriluk, R. (2007). Variability in measurement of swimming forces: A meta-analysis of passive and active drag. Research Quarterly for Exercise and Sport, 78(2), 32-39. Takagi, H., Shimizu, Y., Onogi, H., & Kusagawa, Y. (1998). The relationship between coefficients of drag and swimming performance. II Australia and New Zealand Society of Biomechanics Conference (Abstract), 56. Toussaint, H.M., de Groot, G., Savelberg, H.H.C.M., Vervoorn, K., Hollander, A. P., & van Ingen Schenau, G. J. (1988). Active drag related to velocity in male and female swimmers. Journal of Biomechanics, 21, 435-438. White, J.C. & Stager, J.M. (2004). The relationship between drag forces and velocity for the four competitive swimming strokes. Medicine and Science in Sports and Exercise, 36(5), S9. 323
BiomechanicsandmedicineinswimmingXi Evaluation of Kinaesthetic Differentiation Abilities in Male and Female Swimmers Invernizzi, P.l., longo, s., scurati, r., Michielon, G. Università degli Studi di Milano, Facoltà di Scienze Motorie, Milan, Italy Events longer than 50 meters require some tactical skills in order to manage the increase of fatigue, such as distributing the effort evenly over the whole distance. Kinaesthetic differentiation skills are required to achieve a very high precision of the movements. The repeatability of two procedures, aimed to measure the kinaesthetic differentiation abilities of swimmers was studied and the correlations between the actual performances and the expected performances with respect to gender and to the degree of change in velocity, were observed. Collecting the data in a single day and during four days running resulted in reliable results. Male swimmers seem to differentiate better than females and show a generally higher coefficient of correlation between the actual and the expected performance. Key words: kinaesthetic differentiation, sensory perception, motor control IntroductIon Physiological factors such as strength and power, and technique and the ability to reduce drag, are the main factors determining swimming performance. Furthermore, any event longer than 50 meters requires that swimmers employ some tactical skills, such as distributing effort evenly over the whole distance, in order to manage increasing fatigue. Even highlevel athletes tend to swim too fast the first part of the event compromising the whole performance (Maglischo, 2003), especially during short distance events. The control of swimming pace largely depends on coordinative and on sensory-perceptive abilities. The interaction between feedback and sensory-perceptive information allows full control of the movement. Furthermore, thanks to motor memory, the movement’s regulatory system can precisely differentiate and manage the intensity of effort (Bernstein, 1975). Kinaesthetic differentiation abilities seem to have a progressive development with age, a plateau during puberty, an increase from 16 years with a peak between 19 and 21 years, depending on gender (Hirtz, 1988). Kinaesthetic differentiation skills are thus important to perfect the swim. Thanks to these abilities, swimmers can achieve a very high precision of movement, having good control even when no visual feedback is allowed, bringing the execution of the movement closer to the ideal (Schicke, 1982), improving the “feeling of the water” and thus performing better propulsive actions or better reducing drag forces (Colwin, 2002). This study aimed to verify the repeatability of measuring and evaluating the kinaesthetic differentiation abilities in good-level swimmers by two different procedures based on simply swimming at different speeds. The correlations between the actual performances and the expected performances were also observed with respect to gender and to the degree of change in speed. Methods Eighteen swimmers aged 13 to 19 years, of regional to national level, participated in this study: 8 male swimmers (mean±SD, age 15.38±1.84 years, height 168.9±11.7 cm, weight 57.6±13.3 kg, BMI 20.0±2.4 kg·m - 2 ) and 10 female swimmers (mean±SD, age 15.75±1.39 years, height 167.8±6.0 cm, weight 57.9±8.8 kg, BMI 20.5±2.8 kg·m -2 ). To measure their kinaesthetic differentiation ability, the subjects performed a number of 25m front crawl trials at different paces corresponding to 50% and 80% of the maximum speed. 324 Each trial started without pushing-off the wall, the swimmer being supported in a streamlined, prone position. First, the swimmers performed a 25m front crawl trial at maximum speed (25m 100% ). The speed corresponding to 50% and 80% of maximum was immediately calculated by an MsExcel worksheet and communicated to the swimmer. Afterwards they were asked to perform a total of eight 25m swims as closely as possible to the requested speed (4 trials at 50% and 4 trials at 80% respectively). The time of each 25m performance and the time for the central 10 meters (from 7.5m to 17.5m) were recorded. Feedback was given after each trial: the swimmers were advised of their performance on a scale of 1 to 10, 10 corresponding to the 100% (maximum), 8 for the 80% effort, and 5 for the 50% effort. This was done in order to make the perception of speed easier for the younger swimmers. Two different procedures were employed: i. Procedure 8/1, executing the protocol in a single day; ii. Procedure 8/4, executing the protocol over four days. 8/1: The swimmers performed 4 consecutive 25m front crawl trials at 50% of the maximum followed by 4 consecutive 25m front crawl trials at 80% of maximum on the same day. Full recovery was allowed between trials and feedback from the previous performance was given, as explained above. 8/4: The swimmers performed two trials per day, over four days. Each day, a 25m front crawl trial at 50% of maximum and after full recovery one at 80% of maximum, were performed. Feedback of the results from the previous day was provided before starting. Statistical analysis was carried out using SPSS 13.0 software. The normal distribution of the data was verified by the Shapiro-Wilk test and parametric statistics were applied. Test validity was analyzed by the Intraclass Correlation Coefficient (ICC). Afterwards, by both gender and procedure (8/1 and 8/4), the Pearson’s Correlation Coefficient between the actual and the expected performance was calculated. results The validity and the repeatability of the procedures employed in this study are shown in Table 1. Table 1. Validity of the test (ICC) Group 1 % Changes in the mean 2.36 Typical error 5.92 Intraclass r (ICC) 0.77 The ability of the swimmers to perform 25m front crawl at a given speed corresponding to 50% and 80% of their maximum is illustrated in Tables 2 and 3: correlations with the 25m 100% front crawl trials are shown. Both procedures (all trials in a single day and two trials in four days running) have been considered. Table 2. Correlation (Pearrson’s) by gender in the 8/1 procedure between the performance and the expected speed at 50%max and 80%max. Values refer to the whole distance (25m) and to 7.5m to 17.5m (10m). * = p
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average VO2 measured during resting
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Figure 2. Repeatability of the LTin
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Pahlen Norge AS Pahlen Norge AS Cha
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