Influence of countermovement depth on net force, push-off time, vertical impulse and performance during jumping.

The purpose of this study was to investigate the influence of push-off distance on maximal jump height and to characterize the relationships between vertical jump mechanical parameters. Seventeen CrossFit athletes performed maximal countermovement jumps on two force-plates, with four different push-off distances induced by different countermovement depths. Results confirmed that push-off distance and maximal jump height were related by a quadratic relationship, and that exists an individual push-off distance maximizing maximal jump height. Furthermore, the increase in push-off distance was associated with an increase in the time of push-off and a concomitant decrease in the mean vertical external force, changing the relative net vertical impulse and so maximal jump height. An almost perfect negative linear relationship was observed between mean vertical external force and time of push-off (r = -0.99, p = 0.006), mathematically resulting in a quadratic relationship between relative net vertical impulse and time of push-off (r = 1.00, p < 0.001). This negative linear relationship could be explained by changes in joint angles and velocities associated with an increase in push-off distance, modifying joint torque production capacities during vertical jumping. This provides new insights to characterize vertical jump mechanical parameters and ways to optimize training and jump performance.