Track 6. Sport Biomechanics - Joint ISB Track

6944 Mo-Tu, no. 88 (P62) The postural control in Tai Chi push-hand Y.-B. Huang 1 , L.-H. Wang 1,2, C.-J. Lin 1 , C.-'~ Tsai 1 , F.-C. Su 1 . 1Institute ef Biomedical Engineering, 2Department of Physical Education, National Cheng Kung University, Tainan, Taiwan

Tai Chi Chun (TCC), one of traditional Chinese martial arts, is a low-impact exercise stressing the control over one's body's center of mass displacement and postural alignment. The center of pressure (COP)-center of mass (COM) variable, the distance between COP and COM, has been widely used to estimate the ability of postural control. The quantitative study on postural control during performing push-hand in TCC is still not available. The purpose of this study was to study the postural control during performing Tai Chi push hands. Nine male Tai Chi masters were recruited in this study. The motion analysis Eagle digital system (Motion Analysis Corp., Santa Rosa, CA, USA) was used to capture the whole body movements during performing the stable-step Tai Chi push-hand with 31 retro-reflective markers placed on selected anatomic landmarks on the head, trunk, upper and lower extremities. In addition, two force plates were synchronized to measure the ground reaction forces for both legs, respectively. The results showed that all subjects' COP trajectories moved smoothly and concentrated on a trail. The mean length ratio between the path length of COP and the width of two heels is 87%. The COP trajectory is related to each subject's skill level. Furthermore, it was also found that the mean COP- COM variable was 0.05±0.02 m (11% of stance width) which is much smaller than that, 0.25 m, during level walking. The mean COP-COM variable in Tai Chi push hands is 6.5% and 7.5% of stance width in mediolateral (ML) and anteroposterior (AP) directions, respectively. With small sway or deviation from the path the COP, all subjects maintained an upright posture while traveling slowly and steadily from one movement to another.

6945 Mo-Tu, no. 89 (P62) The comparison of kinematics characteristics between single and successive kicking techniques for the taekwondo player with an olympic medal: a case study Y.-H. Nien 1 , J.-S. Chang 2, W.-T. Tang 1 . 1Institute ef Coaching Science, National College of RE. & Sports, Taoyuan, Taiwan, 2Department of Sports Training Science-Combats, National College of RE. & Sports, Taoyuan, Taiwan

The competition rules of Taekwondo was modified to prefer the successive kicking which can get more points since the last official event of the Olympic game. The rule encourages the number of attacks relative to the intensity of attacks. In previous studies, the researchers were focus on single kicking technique, not successive kicking yet. The successive kick is composed of several single roundhouse kicks the most frequently used technique in compe- titions. However, the training of successive kicking technique depends on coach experiences at present, the guidelines are not clear. Therefore, the purpose of this study was to analyze the differences of kinematics characteristics between single kicking technique and successive kicking technique through Motion Analysis System. The subject is the elite athlete of National Taekwondo Team of Taiwan who won many medals of Taekwondo games at international level (include 2004 Olympic Games). In experimental setup, forty-three markers were attached on the skin of the subject's each segment and joint, and eight markers were placed on the target for the kicks. The Motion Analysis System with 7 high speed cameras (Eagle cameras, Motion Analysis Corporation, Santa Rosa, CA, USA) were used to collect the kinematics data through tracking the makers automatically, and then the timing sequence of peak joint velocity for each lower limb were derived from the time series. The results were: 1. The sequence of the peak joint velocities for the lower extremity were hip, knee, and ankle, which were in accord with the kinematics chain of human exercise which smaller joints move after bigger joints move for both type of kicking techniques. 2. The successive kick was larger than the single roundhouse kick in the shoulder-hip-axis projected angle on horizontal plane. The results suggest that the successive kicking movement perform more trunk twist which may contribute to balance the lower extremity round kick motion through the conservation principle of the angular momentum.

4015 Mo-Tu, no. 90 (P62) One repetition maximum prediction from a submaximal performance in weight l i f t ing

M. Hannula, J. Jauhiainen, S. ,~ij~l& Medical Engineering Research Center, Oulu Polytechnic, Finland

The repetition maximum (RM) is an important parameter in training program planning in weight lifting. It can be indirectly assessed by first performing lifts with submaximal weight until exhaustion and then by estimating the RM

6.9. Sport Analysis $563

with regression equations [1,2]. In this study the estimation of the RM on the basis of only one submaximal lift was examined. The estimation was based on analysis of the acceleration during the lift, in which the RM was estimated with a equation RM = (amax/9.81 m/s 2) m, where amax was the maximum acceleration (including gravity) during the lift and m the submaximal weight. To evaluate the hypothesis 30 subjects (2 women, 28 men, age 21±7 years, height 178±6cm, weight 74±11kg) were examined in bench press and dumbbell concentration curl. In data collection the subjects were equipped with a wristwatch including a 3-axis accelerometer. Before data collection the subjects were asked to estimate their current RM's. After this the measurement wristwatch was worn on and the measurements were performed by using about half of the questioned maximum as a load in submaximal lift. The data was analyzed by first detecting the maximum accelerations amax in each lift. Next the RM estimates were calculated. The mean absolute error after linear correction in RM prediction was 7.1% and 9.1% for bench press and dumbbell concentration curl. In light of other studies this RM prediction accuracy is competitive. The hypothesis of this study seemed to be true, however some refinements for the estimation equation, e.g. linear correction coefficients, are needed.

References [1] Mayhew JL, Ball TE, Arnold MD. Prediction of 1-RM bench press from submax-

imal bench press performance in college males and females. J Appl Sports Sci Res 1989; 53: $73.

[2] Hoeger VVWK, Hopkins DR, Barette SL, Hale DE Relationship between rep- etitions and selected percentages of one repetition maximum: A comparison between untrained and trained males and females. Journal of Applied Sport Science Research 1990; 4: 47-54.

5137 Mo-Tu, no. 91 (P62) Flying ball trajectories are anticipated in basketball throwing B. Pflanz 1,3, H. Wagner 1,3, U. Jungnickel 2, P. Maisser 2, R. Blickhan 1 . 1Institute of Sports Science, Friedrich-Schiller-University, Jena, Germany, 2Institute of Mechatronic, Technical University, Chemnitz, Germany, 3Institute of Sports Sciences, Westf#lische Wilhelms-University, MEmster, Germany

Introduction: To hit the basket in basketball the ball needs suitable take- off conditions in position and velocity. The take-off condition must be actively generated by adequate coordinative patterns of the thrower during a ball ac- celerating phase. In this study our objective was to investigate the preparatory kinematics of goal directed throwing to reach suitable take-off conditions. We assumed that the subjects may anticipate the envisioned flight trajectories (EFT) of the ball. Methods: Basketball free throws were performed by seven male sport students with different basketball expertise. Ball kinematics was obtained by three- dimensional motion analysis (Qualisys, 240Hz).The parabolic trajectory of the centre of the flying ball was extrapolated to prior take-off. Horizontal and vertical differences in position and velocity components of the measured and extrapolated trajectory were computed. Furthermore, the possible variability in take-off parameters was estimated that would still hit the basket successfully. This variability was compared to the experimentally obtained differences. Results: It was found that in position the measured ball trajectory approxi- mated the EFT after 39% of the whole length of the acceleration path, i.e. for 61% of the measured trajectory the ball would hit the target. Regarding velocity 92% of the acceleration path was needed to obtain suitable ball release speed. Conclusion: It turns out that the launch velocity seems to be the critical parameter in a successful free throw compared to position [1]. Therefore, the attention of the subjects should be addressed towards the right launch velocity, whereas suitable launch positions are obtained more easily.

References [1] Brancazio EJ. Am J Phys 1980; 49(4).

6775 Mo-Tu, no. 92 (P62) Kinematic and electromyography analysis of lower extremity in Tai Chi push-hand L.-H. Wang 1,2, C.-J. Lin 1 , '~-B. Huang 1 , E-C. Su 1 . 1Institute efBiemedical Engineering, 2Department of Physical Education, National Cheng Kung University, Tainan, Taiwan

The push-hand in Tai Chi Chuan (TCC) is an important skill to make the op- ponents lose their own balance while stability is maintained through defensive position changes. The push-hand movement consists of four events, fend- off, stroke, push, and press movements. How do the Tai Chi masters sense and adapt themselves to their opponent's demands without loosing their root? Postural muscle synergies are still unknown. Therefore, the purpose of this study was to investigate kinematic behavior and muscle activation of the lower extremity during performing Tai Chi push-hand. Nine male community-dwelling adults with push-hand practice for 3.8±6.5 years were recruited in this study. The motion analysis Eagle digital system