LEG STIFFNESS CHANGES IN DROP JUMPS WITH DIFFERENT STRETCH AMPLITUDE
Keywords: leg stiffness, EMG magnitude, stretch reflex
AbstractThe purpose of this study was to investigate the adjustment of leg stiffness and the relative electromyography (EMG) magnitude of different phases with shallow and deep drop jump (DJ) in order to understand the neuromuscular and contraction characteristics of different stretch amplitudes of SSC movement. There were 12 subjects tested in this experiment including jumpers and volleyball players whose ages are 20.5±1.93, heights are 181.01±6.23cm and weights are 71.95±4.93Kg. Kistler forceplatform, PEAK high speed video camera and EMG Biovision system were used to record the ground reaction force, kinematics data and the EMG signals of gastrocnemius and rectus femoris. The results of this study were that the leg stiffness between two different drops jump had the significant difference at the concentric and transmission phases in the progressive loads (p<0.05). It was suggested that the result observed was the interventions of stretch reflex which favor the transmission of force and release of stored energy. However, autogenetic inhibition of the tonic stretch reflex occurred at the 80cm of drop height. It was recommended to avoid the high load intensity which had the disadvantages for the enhancement of plyometric training.
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