Abstract
This study assesses in vivo and noninvasive human lower limb dynamic stiffness at different muscle stretch-shortening cycle (SSC) on maximum vertical jump (MVJ) with long, short and without countermovement. A small sample of n=6 healthy young adult male students of sports and physical education degree without past injuries, specific training or sports record were assessed after informed consent according to the world medical association declaration of Helsinki. Subjects were weighted (76.7 ± 9.3) kg and their height measured (178.9 ± 6.3) cm performing each three trials of MVJ namely squat jump (SJ), countermovement jump (CMJ) and drop jump (DJ) from a step with 40 cm height. Ground reaction forces (GRF) were acquired during impulse phase with AMTI force plate BP2416-4000 CE and Mini Amp MAS-6 amplifier at 1000 Hz. Vertical acceleration (az) of whole body center of gravity (BCG) obtained from resultant vertical ground reaction force (RFz) was time integrated twice for calculation of vertical displacement (Δz) of BCG and dynamic stiffness obtained from slopes at different segmented subphases of RFz mass normalized RFz/m vs Δz plot during impulse phase. Results of vertical dynamic stiffness during impulse phase point for inter-subject similarities at each type of MVJ and statistical significative differences (p<0.05) between SJ, CMJ and DJ with impact on MVJ optimization.
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