Biomechanics and Medicine in Swimming XI

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tive indicators showed a similar trend (F relEBK, I mp F relEBK and Favg relEBK – 23.26, 24.30 and 19.34 %, respectively), while the only variation of the results with respect to the homogeneous group was shown in RFD relEBK (39.21 %). The descriptive and variation indicators can be used as scientifically valid for further comparative analysis. The main force that keeps the water polo players suspended in the water while performing other skills is hydrodynamic lift force, which is caused by the flow of water over the foot and leg of the athlete. With respect to the obtained descriptive indicators, it can be maintained that the interval at 95% likelihood in assessing the training level of the analyzed tethered pulling force characteristics realized with 10s maximal intensity in male top senior national level water polo players was as follows: Time EBK = 441 – 555 ms; F maxEBK = 155 – 227 N; F avgEBK = 119 – 162 N; I mp F EBK = 59 – 87 N⋅s; RFD EBK = 238 – 436 N⋅s -1 ; Hz EBK = 107 – 137 Slk⋅min -1 for absolute values of the single leg eggbeater kick. At the reliability rate of 95%, the descriptive variable results yielded the following relative values: F relEBK =1.76–2.83 N⋅kg -1 ; Favg relEBK =1.36–2.02 N⋅kg -1 ; I mp F relEBK =0.67–1.09 N⋅s⋅kg -1 ; RFD relEBK =2.49–5.72 N⋅s -1 ⋅kg -1 for relative values of the single leg eggbeater kick. With respect to the basic kinetic indicator, i.e., the duration of a single eggbeater kick, it was established that it ranged from 441 to 555 ms at the likelihood level of 95% (average Time EBK value ± SD value). As compared to the results published by Marion & Taylor (2008), the time for one complete eggbeater kick cycle was between 0.5 sec and 0.65 s. However, here the authors studied the eggbeater kick technique with the athletes in vertical position, while in the present study the water polo players realized the maximal pull force within 10 s in the semivertical chest-forward position. It is possible that the ensuing difference in the duration of a single leg cycle was due to the different measurement methods as well as to the nature of the task and the intensity of legwork under load. A study of the vertical force exerted during the eggbeater kick in water polo concluded that the vertical force of the kick ranged from 60 to 112 N (Yanagi, Amano et al. 1995, as cited in Marion & Taylor, 2008). According to Marion & Taylor (2008) for an athlete with a weight of 600 N, the eggbeater contributes in 10-20% of the upward force required to balance the body weight. The current study established that senior top water polo players’ average values of maximal single leg eggbeater kick pull force (peak force) can be achieved with maximal effort in 10 s at the average level of 190±36 N, i.e. ranging between 155 and 227 N with 95% reliability. Moreover, the rate of force development of the eggbeater kick was shown to be at the level ranging between 238 – 436 N⋅s -1 with 95% likelihood level. In our results, the average BM was 84.5 kg and the pulling force realized by the given method was at the level of 23.40±5.44 % of the subjects’ BM, i.e. within the reliability range of 18.0 to 28.8%. Presumably, all the measured kinetic characteristics of legwork in the given water polo technique are due to the years of the players’ adaptation to the exertions of training and competition so that the experimental results can represent an actual model of the players’ abilities to cope with the task given in the test. New water polo rules introduced in 2006 resulted in more intensive competitor efforts, especially for technical and tactical elements where legwork is the dominant movement (eggbeater, jumps, shots, duel play and defender actions) for which players must be prepared through an adequate system of training (Platanou, 2009). Such data indicate that more intensified training and the introduction of specific changes in the training work are necessary to achieve best results in water polo, especially in vertical and semi-vertical water polo positions. Besides, the approach given here highlights the demand for defining specific methods to test the abilities of water polo players. conclusIon The results indicated the descriptive values of the kinetic characteristics of the 10s maximal tethered eggbeater kick in elite water polo players chaPter2.Biomechanics with regard to the absolute and relative values. The reliability analysis showed that the reliability of measuring the pulling force characteristics of 10s maximal tethered egg beater kick was highly statistically significant at 96.81%, with ICC at single measures = 0.918, and at ICC average measures = 0.994. It was also established that only two variables of the measured value showed statistically significant change in the time interval of 10s, namely FmaxEBK and FavgEBK. In our results, the average tethered pull force peaked at 23.40±5.44 % of the subjects’ body mass. Moreover, the resulting data could also help towards the development of water polo training technology, and the establishment of a new method to test the specific leg fitness in elite senior water polo players. reFerences Dopsaj, M., Matkovic, I., Thanopoulos, V., & Okicic, T. (2003). Reliability and validity of basic kinematics and mechanical characteristics of pulling force in swimmers measured by the method of tethered swimming with maximum intensity of 60 seconds. FACTA UNI- VERSITATIS: Series Physical Education and Sport, 1(10):11-22. Dopsaj, M., & Thanopoulos, V. (2006). The structure of evaluation indicators of vertical swimming work ability of top water polo players. Revista Portuguesa de Ciencias do Desporto (Portugese Journal of Sport Sciences), 6(2), 124-126. Gastin, P. B. (2001). Energy system interaction and relative contribution during maximal exercise. Sports Medicine, 31(10), 725-741. Marion, A., & Taylor, C. (2008). The technique of the eggbeater kick. http://www.coachesinfo.com/ (09.01.2010). Platanou T. (2004). Time motion analysis of international level water polo players. J Hum Mov Stud, 46, 319-331. Platanou, T. (2009). Cardiovascular and metabolic requirements of water polo. Serb J Sports Sci, 3(3), 85-97 Sanders, R. (1999). Analysis of the eggbeater kick used to maintain height in water polo, J Appl Biomechanics, 15, 284-291. Smith, H. K. (1998). Applied physiology of water polo. Sports Med, 26, 317–334. Sidney, M., Pelayo, P., & Robert, A. (1996). Tethered forces in crawl stroke and their relationship to anthropometrics characteristics and sprint swimming performances. J Hum Mov Studies, 31, 1-12. Takagi, H., Nishigima, T., Enomoto, I., & Stewart, A. M. (2005). Determining factors of game performance in the 2001 World Water Polo Championships. J Hum Mov Stud, 49 (5), 333-352. 71
BiomechanicsandmedicineinswimmingXi Motor Coordination During the Underwater Undulatory Swimming Phase of the Start for High Level Swimmers elipot, M. 1, 2 , houel, n. 2 , hellard, P. 2 , dietrich, G. 1 1 Université Paris Descartes, Paris, France 2 Fédération française de natation, Paris, France The aim of the present study was to identify the main motor coordination involved during the underwater undulatory swimming phase of the start. Twelve French high-level swimmers took part in this study. Swimmers were filmed during the entire underwater phase of the start (i.e. fifteen meters from the start platform). Specific anatomical landmarks were identified on the body of the swimmers and 2D space coordinates of these landmarks were calculated. Cross correlation functions were used to investigate the motor coordination between the actions of the hip, the knee and the ankle. Results show that high-level swimmers regulate the leg amplitude thanks to a strong synergy between the hip and the ankle and an independent action of the knee. Key words: Motor control, start, underwater undulatory swimming INTRODUCTION High-level athletes are characterised by superior tactical, physical and technical levels. Improving one of these factors will lead to a performance improvement. As in many other sports, swimming performance is strongly linked to the technical level of the swimmers. Swimming performance optimisation requires an accurate analysis of the swimmers’ movement. Biomechanics and motor control sciences give useful tools to realise such analysis. Motor control theories, and more especially the joint synergies theories, will indeed help to understand how high level swimmers are able to produce specific, appropriate and efficient motor pattern. Many previous researches have already shown that start performance is determinant to achieve a good race performance. Depending on the studies, start performance is defined as the time to complete the 10 or 15 first meters from the start wall (Alves, 1993; Arellano et al., 1996; Mason and Cossor, 2000). The start consists of 3 phases: the impulsion phase, the aerial phase and the underwater phase (Maglischo, 2003). This underwater phase of the start could be divided in 2 phases, i.e. the glide phase and the underwater undulatory swimming phase (Maglischo, 2003). During the glide, swimmers aim to keep the supra-maximal velocity created during the impulsion and aerial phases as high as possible and as long as possible. A previous study has already shown that during the glide phase high level swimmers presented a strong joint synergy between the shoulders, the hip and the knee (Elipot et al, 2009). It seems that with this synergic action of those three joints high level swimmers are able to hold a streamlined position during the whole glide phase. Hydrodynamic resistance are decreased and supra-maximal velocity is kept longer. During the underwater undulatory swimming, the swimmers’ aim is to produce velocities with leg action. Swimmers have then to find the optimal compromise between the amplitude and the frequency of the leg undulatory movements (Arellano, 2008). Swimmers have to find the optimal compromise between propulsion force creation and hydrodynamic resistance decrease. Identifying the motor coordination during this underwater undulatory swimming phase of the start is a major step to understand and optimise this phase. The aim of this study was to determine the motor coordination that high-level swimmers are able to produce during the underwater undulatory swimming phase of the start. 72 Biomechanics and Medicine XI Chapter 2 Biomechanics Swimmers have then to find the optimal compromise between the amplitude and the frequency of the leg undulatory movements (Arellano, 2008). Swimmers have to find the optimal compromise between propulsion force creation and hydrodynamic resistance decrease. Identifying the motor coordination during this underwater undulatory swimming phase of the start is a major step to understand and optimise this phase. Methods The aim of this study was to determine the motor coordination that high-level swimmers are able to produce during the underwater undulatory swimming phase of the Subjects start. and instructions: Twelve male swimmers participated in this study. All were informed of METHODS the Subjects aim of and the instructions: study and signed a consent form. All participants were high-level Twelve male swimmers participated and were in members this study. of All the were French informed National of the aim of Swim- the study and signed a consent form. All participants were high-level swimmers and were ming Team. Swimmers’ characteristics are summarized in Table 1. members of the French National Swimming Team. Swimmers’ characteristics are summarized in Table 1. Table 1. Swimmers’ general characteristics (n = 12). Table 1. Swimmers’ general characteristics (n = 12). Height (m) Weight ( kg) Best performance (freestyle) 50-m (s) 50-m (%) 100-m (s) 100-m (%) Mean 1.83 76.1 24.39 116.47 52.26 111.4 SD 4.89 5.18 1.26 6.02 1.68 3.57 Swimmers were asked to perform 3 grab starts as fast as possible. Only the best start was analysed (i.e. the best time to complete 15 meters from the start wall). All swimmers were regularly trained to perform this kind of start and use it during competition. Experimental set up and data analysis: Swimmers were filmed by 4 mini-DV camcorders (576x720 pixels) during the whole underwater phase of the start (i.e. fifteen meters from the start platform) (Fig. 1). The camcorder 1, 2 and 3 were placed the swimming pool portholes and the camcorder 4 was placed in the water in a waterproof housing. The camcorders position has been chosen so as to minimise to reconstruction error due to optical distortions (Snell low). All camcorders were synchronised using a light signal and sampling frequency was 25Hz. Images were deinterlaced and odd and even fields were both used. Nine anatomical landmarks were identified on swimmer’s body: the toe, the lateral malleolus, the knee, the iliac spine, the acromion, a finger hip, the wrist, the elbow and the centre of the head. To minimise the error during the digitising process, only the right side of the swimmers has been identified. Both sides were supposed to be symmetric. Using a modified DLT 2D technique (inspired from Drenk et al., 1999) and the Dempster anthropometric data (Dempster, 1959), joints’ positions and swimmers’ centre of mass position have been calculated. Reconstruction error was calculated as indicated by Kwon and Casebolt (2006). Mean reconstruction error was 6.2 mm and maximal reconstruction error was 12.2 mm. Data were filtered using a Butterworth II filter (Winter, 1990). Cut-off frequencies were included between 5 Hz and 7 Hz. Swimmers were asked to perform 3 grab starts as fast as possible. Only the best start was analysed (i.e. the best time to complete 15 meters from the start wall). All swimmers were regularly trained to perform this kind of start and use it during competition. Experimental set up and data analysis: Swimmers were filmed by 4 mini-DV camcorders (576x720 pixels) during the whole underwater phase of the start (i.e. fifteen meters from the start platform) (Fig. 1). The camcorder 1, 2 and 3 were placed the swimming pool portholes and the camcorder 4 was placed in the water in a waterproof housing. The camcorders position has been chosen so as to minimise to reconstruction error due to optical distortions (Snell low). All camcorders were synchronised using a light signal and sampling frequency was 25Hz. Images were deinterlaced and odd and even fields were both used. Nine anatomical landmarks were identified on swimmer’s body: the toe, the lateral malleolus, the knee, the iliac spine, the acromion, a finger hip, the wrist, the elbow and the centre of the head. To minimise the error during the digitising process, only the right side of the swimmers has been identified. Both sides were supposed to be symmetric. Using a modified DLT 2D technique (inspired from Drenk et al., 1999) and the Dempster anthropometric data (Dempster, 1959), joints’ positions and swimmers’ centre of mass position have been calculated. Reconstruction error was calculated as indicated by Kwon and Casebolt (2006). Mean reconstruction error was 6.2 mm and maximal reconstruction error was 12.2 mm. Data were filtered using a Butterworth II filter (Winter, 1990). Biomechanics Cut-off and frequencies Medicine XI were included Chapter 2 Biomechanics between 5 Hz and 7 Hz. Camcorder 1 Camcorder 2 Camcorder 3 Figure 1. Experimental set up Figure 1. Experimental set up To avoid between-subjects variations due to the slope of the trajectory to reach the To water avoid surface, between-subjects data were expressed variations in a (O’, due n, t to ,b) the local slope reference of the frame trajectory attached to the swimmers’ centre of mass and with n collinear to the velocity vector and t perpendicular to reach the water surface, data were expressed in a (O’, n, t ,b) local to n (Fresney frame of reference). During the whole underwater phase, the velocity of reference the centre of frame mass, attached the joint positions, to the swimmers’ velocities and centre angles of for mass the hip, and the with knee n and the collinear ankle, the to angles the velocity between vector the x-axis and and t perpendicular the limbs (angle to of n (Fresney attack) were frame calculated. of Only reference). the joints longitudinal During the and whole vertical underwater positions were phase, expressed the velocity in the original of the global frame (O, x, y, z). centre Motor of mass, coordination the joint was positions, investigated velocities by computing and angles the cross for correlation the hip, the functions knee between and all the ankle, calculated the kinematics angles between variables. the These x-axis kinematic and the data limbs were (angle represented of in form attack) of were time-dependent calculated. signals. Only the Results joints were longitudinal obtained using and Matlab vertical software posi- (The Matworks Inc., USA). Level of confidence was set at 95% (p
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Pahlen Norge AS Pahlen Norge AS Cha
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