The purpose of this study was to investigate the effects of different stretch amplitudes (angular displacements) on the performance and electromyographic (EMG) activity during drop jumps (DJs). The AMTI force platform, the Biovision electrical goniometer, and EMG system were used to record the ground reaction forces, knee angular displacement, and the EMG signals of the rectus femoris. The EMG data were treated by different data-processing methods: the biphase and triphase data-processing methods. The results revealed that the short-stretch DJs had a larger passive force, a higher eccentric end force, a higher concentric average force, and a faster eccentric angular velocity showing a more efficient stretch-shortening cycle (SSC) mechanism in using elastic energy and reactive properties than the long-stretch DJs. Therefore, the short-stretch DJs are recommended in training for the SSC movement. However, the results of biphase data-processing EMG method did not support this conclusion because there was no significant difference between long-stretch DJs and short-stretch DJs by using the biphase data-processing method, whereas the triphase method did support this conclusion and demonstrated that short-stretch DJs are more efficient.

The purpose of the present study was to evaluate leg muscular regulation and neuromuscular activation by investigating the stiffness and EMG amplitude between normal vision students and visually impaired students. Ten normal vision (age: 24.3 ± 2 years; 171.5 ± 4.6; mass: 65.9 ± 8.0) and 10 visually impaired students (age: 23.2 ± 2.4 years; 163.4 ± 9.6; mass: 62.8 ± 15.0) served as subjects. An AMTI force platform (1200 Hz) and a Peak Performance high speed camera (60 Hz) were used synchronously to record the ground reaction force, the kinematic parameters and EMG signals of lower extremity during the subjects stepped down from height 20, 30 and 40 cm. After treating the data and discussion, the conclusions were obtained. The regulation of neuromusclar system of the impaired is less efficient compared to the normal one because of softer stiffness and lower EMG activity.

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