Biomechanics and Medicine in Swimming XI

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ω y (deg/s) ω x (deg/s) t glide25 Parameter selection for a backstroke trial t stroke25 t pp pω x t turn pω y t glide50 t stroke50 time (s) time (s) Figure 2: parameter selection for backstroke using its most descriptive angular velocities, ω x and ω y . The same parameter selection can be adopted for the further axis and for the other swimming styles. Apart from the starting phase, it is possible to easily recognise the underwater gliding and the stroke phase of the first 25m lap, the turning phase and the final lap with the relevant gliding and stroke phases. Local peaks for each angular velocity, pω x and pω y , during the turning phase were also highlighted, together with the t turn and t pp durations. ω z (deg/s) ω y (deg/s) t glide25 Parameter selection for a butterfly trial t stroke25 pω y pω z t turn t glide50 t stroke50 time (s) time (s) Figure 3: parameter selection for a butterfly trial using its most descriptive angular velocities, ω y and ω z . It is possible to outline several differences from the previous style, particularly in the stroke phase and in the turning phase, where the negative ω z peak specifically characterizes the open-turn technique executed by the butterfly swimmer. Starting from the sensor output, the following further parameters were defined. According to the literature, the stroke rate is defined for each lap (sr25 and sr50 ) as number of stroke cycles per minute. Furthermore, aiming at outlining the strategy undertaken by the swimmer in choosing the duration of both gliding and stroke phases for the two laps, the tglide synthetic indices r25 and r50 were defined as follows: r = . An r index tstroke near 1 indicates that the two phases have a similar duration (e.g. for backstroke), whereas values less than 0.5 are expected for breaststroke swimmers. chaPter2.Biomechanics results Each swimmer completed the execution without problems and did not experience any difficulty in using the instrumental apparatus. Results for the eight swimmers are listed in Table 1. Positive and negative pω values are according to the convention in Fig. 1. Biomechanics and Medicine in Swimming XI Chapter 2 Biomechanics b Table 1. Results obtained for the four swimming styles for each selected parameter. Table 1. Results obtained for the four swimming styles for each selected parameter. pωx (deg/s) pωy (deg/s) pωz (deg/s) tpp (s) tturn (s) sr25 (cycle/min) r25 sr50 (cycle/min) r50 tchr (s) Free M F -241 -310 565 324 -111 -69 0.95 0.92 1.35 1.48 60.08 55.17 0.36 0.44 55.65 51.60 0.12 0.11 25.7 27.8 Back M F -352 354 344 321 -18 -47 1.02 1.16 2.15 2.36 67.67 46.81 0.99 0.70 56.07 44.44 0.65 0.56 26.7 32.0 Breast M F -205 -140 -379 -296 -330 -128 0.46 0.42 1.16 1.26 61.71 52.82 0.36 0.29 57.24 44.02 0.16 0.26 29.8 35.8 Fly M F -230 -119 -321 -265 -260 -238 0.54 0.66 1.24 1.14 60.26 61.46 0.41 0.51 59.29 57.04 0.28 0.17 25.6 29.5 DISCUSSION dIscussIon The present study verified the feasibility to use wearable inertial sensor devices to characterise turning, gliding and stroke resumption in swimming. The novelty of the approach is constituted by the use of gyroscopes to measure angular velocities and by the consequent easy description of swimming rotational movements. If used in conjunction with the available measured linear accelerations, several biomechanical parameters can be extracted that increase the knowledge about each swimming style and/or about the strategy adopted by each swimmer. Several quantitative parameters were selected from the sensor device output: the choice reflected the need to characterise each swimming style and offer possible parameters to describe the way each athlete executes his/her swimming exercise. Highest pωy were found for freestyle in both genders. This circumstance is directly related to the well-known highest velocities usually obtained in this swimming style at the end of the 25m lap. This parameter was higher for males than for females, as it happens usually for mean velocity, even if related differences are slighter than for linear velocity. In fact, the two parameters are linked by the equation - v = ω*R - being R the distance between the most external point and the rotational axis and, thus, related to the individual flexibility. Considering that females are usually more flexible than males, thus more able in reducing R, it is possible to argue that a higher R for female compensates the higher mean velocity usually obtained by male swimmers. The sign of the rotation depends upon the style turning technique: freestyle and backstroke use a ecutes flip-turn his/her technique, swimming thus involving exercise. a positive rotation about the y axis, vice-versa breaststroke and butterfly use an open-turn that involves a negative rotation about the same axis corresponding to the recall of the leg before the push-off. Further peak angular velocities, pωx and pωz, characterised differently the other swimming styles. Highest pωx were found for the backstroke flip-turn that is first characterised by a sudden rotation about the cranio-caudal axis, consistently with its theoretical execution. For all styles, the negative peak indicated that every athlete carried out the rotation leading the right arm, thus executing a clockwise rotation about the cranio-caudal axis. This is, in fact, a choice dependent upon the single swimmer. Highest pωz, conversely, were found for both breaststroke and butterfly. This circumstance is consistent with the open-turn technique used for these two styles: after the feet contact on the pool wall, the swimmer suddenly turns the upper body leading the rotation using the right arm, thus generating a clockwise rotation about the z axis (negative pωz peak). The present study verified the feasibility to use wearable inertial sensor devices to characterise turning, gliding and stroke resumption in swimming. The novelty of the approach is constituted by the use of gyroscopes to measure angular velocities and by the consequent easy description of swimming rotational movements. If used in conjunction with the available measured linear accelerations, several biomechanical parameters can be extracted that increase the knowledge about each swimming style and/or about the strategy adopted by each swimmer. Several quantitative parameters were selected from the sensor device output: the choice reflected the need to characterise each swimming style and offer possible parameters to describe the way each athlete ex- Highest pωy were found for freestyle in both genders. This circumstance is directly related to the well-known highest velocities usually obtained in this swimming style at the end of the 25m lap. This parameter was higher for males than for females, as it happens usually for mean velocity, even if related differences are slighter than for linear velocity. In fact, the two parameters are linked by the equation - v = ω*R - being R the distance between the most external point and the rotational axis and, thus, related to the individual flexibility. Considering that females are usually more flexible than males, thus more able in reducing R, it is possible to argue that a higher R for female compensates the higher mean velocity usually obtained by male swimmers. The sign of the rotation depends upon the style turning technique: freestyle and backstroke use a flip-turn technique, thus involving a positive rotation about the y axis, vice-versa breaststroke and butterfly use an open-turn that involves a negative rotation about the same axis corresponding to the recall of the leg before the push-off. Further peak angular velocities, pωx and pωz , characterised differently the other swimming styles. Highest pωx were found for the backstroke flip-turn that is first characterised by a sudden rotation about the cranio-caudal axis, consistently with its theoretical execution. For all styles, the negative peak indicated that every athlete carried out the rotation leading the right arm, thus executing a clockwise rotation about the cranio-caudal axis. This is, in fact, a choice dependent upon the single swimmer. Highest pωz, conversely, were found for both breaststroke and butterfly. This circumstance is consistent with the open-turn technique used for these two styles: after the feet contact on the pool wall, the swimmer suddenly turns the upper body leading the rotation using the right arm, thus generating a clockwise rotation about the z axis (negative pωz peak). Still focusing on the turning phase, tpp and tturn were higher for backstroke, consistently with the backstroke turning technique that includes a rotation (positive if clockwise, negative if counter-clockwise) about the X-axis before the execution of the rotation about the Y-axis. Also, tpp value indicates that flip-turns are characterised by two distinct rotations (about y and x axes), while open-turns are complex movements in which rotations follow each other in a faster way. 165 179
BiomechanicsandmedicineinswimmingXi The use of gyroscopes allowed us to describe, the strategy adopted by each athlete during his/her swimming action, also. This was done using both sr and r parameters. Dealing with stroke rates, sr 50 was consistently lower than sr 25 , circumstance that is presumably related to the appearance fatigue. This parameter was typically lower in females than males, except for butterfly where the female and male swimmers obtained similar sr values. This is due to linear relationship between velocity and stroke frequency: the female butterfly swimmer had a very good performance, thus approaching the execution of the male athlete. Thus, the approach proposed in this paper allowed for the quantification of stroke frequency, but its application to performance analysis needs to be carried out in presence of trials at a constant velocity, where differences could be attributed to a different strategy adopted by the swimmer. Focusing on the ratio between gliding and stroke phases, r 50 was consistently lower than r 25 , which involves a longer gliding phase after the racing start. Highest r 25 and r 50 were found for backstroke and butterfly, consistently with their theoretical style executions. conclusIon Inertial sensor devices integrating both accelerometers and gyroscopes represent a useful tool for performance evaluation in swimming research. Specifically, using gyroscopes represents a promising measurement technique for coaches to investigate how swim turning, underwater gliding and stroke resumption phases are implemented in the different swimming styles. Strength points of the approach are the simple description of the turning kinematics, the possibility to extract multiple parameters useful for performance analysis, the simplicity of use for the operator, the minimal encumber for the athlete. Future steps in this research will take into account the inclusion of further athletes and the definition of further parameter (acceleration peaks, estimation of angles), eventually specific for each swimming styles. reFerences Lyttle AD, Blanksby BA, Elliott BC, Lloyd DG (1999). Optimising kinetics in the freestyle flip turn push-off. Journal of Applied Biomechanics, 15: 242-52 Ohgi Y, Ichikawa H, Homma M, Miyaji C (2003). Stroke phase discrimination in breaststroke swimming using a tri-axial acceleration sensor device. Sports Engineering, 6: 113–123. Pereira S, Vilar S, Goncaves P, Figueiredo P, Fernandes R, Roesler H, Vilas-Boas JP (2008). A combined biomechanical analysis of the flip turn technique. Proceedings of the 26th ISBS Conference: 699-702. Slawson SE, Justham LM, West AA, Conway PP, Caine1 MP, Harrison R (2008). Accelerometer Profile Recognition of Swimming Strokes. The Engineering of Sport 7, 1: 81-88. Takahashi G, Yoshida A, Tsubakimoto S, Miyashita M (1982). Propulsive Forces Generated by Swimmers during a Turning Motion. In Proc. of the Fourth International Symposium of Biomechanics Medicine in Swimming: 192-198. Champaign, Ill.: Human Kinetic Publishers. 180 Influence of Swimming Start Styles on Biomechanics and Angular Momentum Vantorre, J. 1 , seifert, l. 1 , Bideau, B.²,nicolas, G.², Fernandes, r.J. 3 , Vilas-Boas, J.P. 3 , chollet, d. 1 1 C.E.T.A.P.S. EA 3832, Faculty of Sports Sciences, University of Rouen, France 2 M2S, University of Rennes 2, France 3 CIFI2D, Faculty of Sport, University of Porto, Portugal The aim of this study was to analyze how the start style influences angular momentum. The durations of the block and flight phases, body angles at takeoff and entry, kinetic momentum, kinetics, and 15-m time were assessed. The sample was classified according to start style. The flat start showed significantly lower angular momentum (H=14.7±2.92 vs. 18.0±0.67 and 17.5±0.4 for pike and Volkov), shorter flight phase and distance, and a smaller takeoff angle than the two other start styles. The analysis of angular momentum revealed two main strategies to achieve optimal performance: direct entry into the water to reduce the temporal deficit and start swimming early (flat start), and the immediate generation of high velocity to achieve longer flight time and distance in order to compensate for the relative loss of time in the following parts of the start (pike and Volkov). Key words: swimming start, start style, expertise, angular momentum IntroductIon Many studies have compared the different positions on the start block, but few have compared the aerial curve (defined as the takeoff and entry angles, and the body angles at takeoff and entry). The flat start and the pike start (also called the scoop, whip or hole start) have been described (e.g., Maglischo, 2003) but only a few studies have compared the two. Counsilman et al. (1988) showed a longer start time, greater takeoff and entry angles, and a shorter distance to head entry for the pike start than for the flat start. However, this study was carried out in young swimmers from 10 to17 years old and not in elite sprinters. In contrast, Wilson and Marino (1983) showed in elite swimmers a shorter 10-m start time, a greater entry angle, a shorter distance to entry, and a greater hip angle at entry for the pike start than for the flat start. Kirner et al. (1989) had five training sessions for swimmers in which they combined grab/track starts and pike/flat entries and demonstrated that the grab start-flat entry had a shorter 8-m start time and a smaller entry angle than the grab start– pike entry. However, this study did not compare specialists of each start style but instead imposed training in and performance of the four styles; therefore, the 8-m start time may have been influenced by the preferential style of the swimmers. Seifert et al. (in press) studied 11 elite grab starters and front crawl sprint specialists and distinguished four aerial phase profiles. In addition to the flat start (upper limbs almost extended at takeoff and used for impulse in the block phase) and the pike start (greater arm swing and great takeoff and entry angles), they observed two other styles of aerial curve: the Volkov start (shoulders stretched upward and forward instead of arms) and flight start (short block phase but long flight phase due to great leg power). McLean et al. (2000) calculated the angular momentum of the aerial phase, which is generated during the block phase in order to quantify rotation. They analyzed several start relay techniques, with and without one or two steps before taking off from the block. Taking steps before leaving the block resulted in greater takeoff and entry angles (like a pike start) and each step start was characterized by greater body rotation than the no-step start. Pike trajectory or arm swing during the flight phase (Volkov style) thus has an effect on body rotation and consequently on the aerial part of the start. Indeed, the swim start cannot be reduced to generate the greatest forward impulse; the initial position is a blocked
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Pahlen Norge AS Pahlen Norge AS Cha
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