Background: Joint specific stretch-shortening cycle (SSC) potentiation of lower extremity joints at propulsion onset during jump test performance (JTP) can temporally affect SSC potentiation. However, joint-specific SSC potentiation at propulsion onset during JTP is unknown.
Methods: Twenty-two healthy young adults, 12 men and 10 women, performed: vertical jumps (1) with a preliminary countermovement (CMJ), 2) from a squat position held isometrically for 2-3 seconds at the same knee angle of CMJ (SJ), and (3) after landing from a 15 cm high platform (DJ). Kinetics and kinematics of lower extremity joints were collected. The propulsion onset was calculated uniquely for the hip, knee, and ankle joints and defined as the first positive data point (after the eccentric phase) of the joint angular velocity for each respective joint. SSC potentiation was calculated as the ratio of jump height (JH) and joint extensor moments for CMJ/SJ, DJ/SJ, and DJ/CMJ.
Results: JH ratio for CMJ/SJ, DJ/SJ, and DJ/CMJ were >1 (all P< 0.01). Hip, knee, and ankle extensor moment ratio was >1 (all P<0.01) for CMJ/SJ and DJ/SJ, while for DJ/CMJ, extensor moment ratio was >1 only for the ankle (P<0.03). SSC potentiation was greatest at the ankle followed by the hip and knee for CMJ/SJ and DJ/SJ (all P<0.05).
Conclusions: SSC potentiation at propulsion onset was largest at the ankle followed by hip and knee. Our findings emphasize the importance of the ankle versus hip and knee joints regarding SSC potentiation at the very beginning of JTP.
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