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

$564 Journal o f Biomechanics 2006, Vol. 39 (Suppl 1) Poster Presentations

was used to capture the whole body movements during performing push- hand with 31 retro-reflective markers placed on selected anatomic landmarks on the head, trunk, upper and lower extremities. A surface EMG system was synchronized for muscle activities detection of eight muscles of lower extremities. The results showed that the four events occurred at 12%, 29%, 22% and 37% of push-hand cycle, respectively. Three dimensional range of motion of the lower limb joints were measured. The major saggital plane motions were 5.7±16.7 to 38.9±17.5 degrees of hip flexion, 20.9±18.4 to 65.5±9.5 degrees of the knee flexion, and 0.01±15.6 to 16.1±13.1 degrees of the ankle dorsiflexion. The rectus femoris muscles of both legs performed eccentric contraction and contracted when the center of mass moved toward the fore leg. It was found that different TCC trainings might result in different levels of hamstring muscles relaxation. For competition, TCC learners were instructed to distribute more than half of their weight on the fore leg and the muscles of the rear leg were not completely relaxed. In conclusion, this study helps us understand the interaction between muscle activities and posture control in Tai Chi push-hand movement. The outcome may be used for stability training program design in older persons.

6974 Mo-Tu, no. 93 (P62) Biomechanical analysis of three different blocking footwork techniques in vol leybal l : a pi lot study

G. Don~ 1 , E. Zorzi 1 , N. Petrone 2, Z. Sawacha 1 , C. Cobelli 1 . 1Department of Information Engineering, University of Padova, Italy, 2Department of Mechanical Engineering, University of Padova, Italy

Few studies are present in literature dealing with the blocking performance. The purpose of this pilot study was to investigate many kinematic variables involved in the blocking action in three footwork techniques. A stereophotogrammetric system (60 Hz) has been used to film three female volleyball players of A1 Italian League. A morphological classification of the athletes was obtained by means of some Bosco tests [1] (Squat Jump, Counter Movement Jump, Stiffness). Each subject performed three variations of lateral translation: slide step, running step, jab cross-over step, with the task of blocking the lateral spike coming from an opposing player. Jump height, time of lateral movement and jump, body frontal position, centre of mass [2] speed were assessed. A correlation between jump height and blocking time was observed only in the running step technique (R=0.86). Body frontal position trajectories (pelvis and shoulder orientation respect to the net) were synchronized and plotted as function of the percentage of flight time. The time of centre of mass maximum speed was significantly different for the jab cross-over step technique. The individual analysis of each athlete confirms the hypothesis that every athlete should use the technique more adapt to her physical characteristics and role. The analysis helped the athletes in finding their most effective blocking method and the coach in conceiving a training strategy to improve all the three techniques. Future studies with a larger number of subjects will allow to better quantitatively define these blocking techniques.

References [1] Bosco C., et al. Mechanical power test and fibre composition of human leg

extensor muscles. Eur. J. Appl. Physiol. 1983; 51: 129-135. [2] Dempster W.T. Space requirements of the seated operator, W.A.D.C. Technical

Report. 1955; Ohio: Wright-Patterson Air Force Base.

6106 Mo-Tu, no. 94 (P62) Signi f icant d i f ference o f footbal l throw-in movements dur ing footbal l match

S. Jiang, X. Wei. Shanghai University of Sports, Shanghai, China

Introduction: The importance of throw-in is always neglected by most of us in football match. But a proper throw-in in the attacking third may impose great pressure on opponent, and even score a goal. So the aim of this study was to assess the characteristic (insufficiency) in throw-in using kinematics parameters, so as to provide some theoretical basis for the future training. Methods: Eighteen football players were randomly selected from the football class of Shanghai University of Sports. At speed of 100 frames/second, the high-speed camera of the JVC GR-DV L9800 was used to shoot the throw- in movement of above-mentioned football players.The shutter speed was set at 0.004s and the aperture was adjusted according to weather conditions. The SBCAS2 analysis system was used to get the kinematic parameters of each player with respect to 5 times stand-up throw-in and 5 times running-up throw-in. The kinematic parameters were compared with those of 2 other good players. Results: The release angle of some player were too large, while some were too small and the release speed of player was significantly less than that of good players. The walking distance was significantly shorter. The throw-in movements of some players were incoherent.

Conclusions: Significant difference of throw-in movements found between the ordinary players and good football players. So they should emphasize the control of release angle, flexibility and the sequence in which each link imposes force during their throw-in training.

6098 Mo-Tu, no. 95 (P62) Evaluation of soccer-speci f ic f ield tests

D.M. Mirkov 1 , A. Nedeljkovic 1 , S. Jaric 2. 1 The Research Center, Faculty of Sport and Physical Education, University of Belgrade, Serbia and Montenegro, 2Department of Health, Nutrition, and Exercise Sciences, University of Delaware, USA

Introduction: The sport-specific field tests are generally popular due to their simplicity, reduced cost, and a minimal use of equipment. Nevertheless, even within the most popular sport games such as soccer, the tests applied are seldom evaluated. Specifically, although most of them could have a property of face validity, their reliability often remains unknown. The aim of the present study was to assess the reliability of selected soccer specific field tests. Methods: Twenty professional male soccer players from the teams belonging to the I national division participated in the study. The evaluated tests were: standing ball kick, throwing-in, 10m, 20m and 30m sprint, 10 5m running, and the zig-zag running performed with and without the ball. Following the instructions and demonstration, the subjects performed one practice and three consecutive experimental trials of each particular test. One-way analysis of variance (ANOVA) with repeated measures and Tukey post-hoc revealed no systematic bias between consecutive trials of the evaluated tests. Results: The ratio between the limits of agreement and the recorded values revealed the highest relative intra-individual variability in the throwing-in and zig-zag running without ball (2.8% and 2.4%, respectively) and the lowest in 20 m and 30 m running (about 0.6%). However, all tests revealed intraclass cor- relation coefficients ICC >0.80 suggesting high reliability except the standing kick that revealed moderate reliability (i.e. ICC =0.76). Conclusion: Therefore, we conclude that all evaluated tests could be recom- mended for field testing of elite soccer players.

6092 Mo-Tu, no. 96 (P62) Biomechanical research on one circle somersault connection techniques of trampoline

J. Shao, X. Wei. Shanghai University of Sports, Shanghai, China

Introduction: One circle somersault movements are the fundamental perfor- mances of trampoline. Connection techniques are the key points of complete performance's segment. This research aims to gain the general kinematics characteristics by analyzing connection techniques of one circle somersault. Methods: We study the similarities and differences of different direction of somersault, the posture of form and twist of one circle somersault and kinematical character of the same movement connects different one circle somersault moments. Using two high-speed JVC by 100 f/s to shoot one circle somersault movements of six trampoline sportsmen in settle the machine flat surface. No. 1 camera shoots the aerial phase, located at 17 m from trampoline net, the height of camera is 4.6 m. Another shoots the touching net phase, laid at the opposite of No. 1 camera, the distance is 4.7 m, and the height is 0.9 m. Results: (1) In leaving net phase, the hip and ankle angles are larger in front somersault than in back somersault, but the knee angle is smaller. (2) There are different from double somersault that the dropping net angle and leaving net angle are smaller in front somersault than in back somersault. (3) Kinematical characteristics are not different in connecting picked and tucked front somersault, the leaving net angle in straight front somersault is larger than in picked and tucked front somersault; the leaving net angle increase with the twist degree in connecting back somersaults, but the leaving net angle decrease with the twist in connecting front somersaults. (4) In dropping net phase, knee first diminished or kept certain angle then straight. In leaving net phase, knee changed with the direction of connecting, it increases gradually in front somersault and decreases in back somersault. (5) The net and foot accelerate curve in touching net phase shows that the rate of elastic force change is larger in dropping net phase than in leaving net phase. Conclusions: one circle somersault connection techniques of Trampoline de- pends on coordination between the human performance and net deformation.