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The Effects of Different Stretch Amplitudes on Electromyographic Activity During Drop Jumps

Lin, Jenq-Dong1; Liu, Yu2; Lin, Jenq-Charng3; Tsai, Feng-Jen4; Chao, Chun-Yu5

Journal of Strength & Conditioning Research: January 2008 - Volume 22 - Issue 1 - pp 32-39
doi: 10.1519/JSC.0b013e31815f6069
Original Research

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.

1Department of Physical Education, Kainan University, Taoyuan, Taiwan; 2Department of Kinesiology, Shanghai University of Sport, Shanghai, China; 3Graduate Institute of Sport Coaching Science, Chinese Culture University, Taipei, Taiwan; 4Department of Physical Education, National United University, Miaoli, Taiwan; 5Department of Physical Education, Kaohsiung Hospitality College, Kaohsiung, Taiwan

Address correspondence to Yu Liu, yuliu@sus.edu.cn.

© 2008 National Strength and Conditioning Association