[[alternative]]The Biomechanical Study of Lower Extremities During Different Squat Jumps

[[abstract]]There were two purposes in this study. 1. To investigate the effect both on the squat jump performance and on the activities of lower extremities through the design of constraining ankle movement and incomplete extension in the joint. 2. To investigate the factors of the effect by comparing the biomechanical differences between highest and lowest performance in regular squat jump. Ten healthy males were conducted as subjects for this study. Redlake high-speed camera (125Hz；1/625), and Biovision EMG system (1250Hz) were synchronized with Kistler force plate (1250Hz) to collect the biomechanics parameters during the subjects performing squat jump movement. The net muscle joint moments were calculated by using inverse dynamics process. Differences between mean values of jumping performance were evaluated by means of Student's t-test for repeat subjects. Statistical significance was set atα＝.05. The results showed that: 1. The range of motion of the ankle was reduced from 58.01° to 39.10° while the ankle was restricted during squat jump. The ankle contributed to the work reduced from 76.39 J to 59.38 J in the instant of take-off. Besides, the range of motion of the knee was reduced from 86.44° to 75.85°. The knee contributed to the work reduced from 75.58 J to 62.07 J in take off activity. 2.During the lowest performance of squat jump the initiate times of EMG signal on m. vasti, m. gastrocentius, and m. soleus were delayed while compare them to those signals on highest performance of squat jump. Similarly, the peak angular velocity of hip joint was appeared earlier than highest performance, and the peak net muscle joint moment was appeared later than highest performance. These phenomena caused the work of hip joint to reduce from 59.39 J to 50.57 J, and the work of ankle joint to reduce from 76.39 J to 67.98 J in take-off activity.