Differential effects of countermovement magnitude and volitional effort on vertical jumping

The importance of vertical jumping in sport and rehabilitative medicine is widely recognized. Despite the ample use of jump tests to assess neuromuscular function, the differential effects of muscular activation (volitional effort) and strategy (countermovement magnitude) on jumping performance have not been studied. The present study aimed to investigate the differential effects of countermovement magnitude and volitional effort on vertical jump performance. Ten male participants performed a total of 60 countermovement jumps each with three different countermovement knee angles (50, 70 and 90°) and four effort levels (25, 50, 75 and 100% of maximal effort). Kinematics and Kinetics were recorded using Vicon System together with a force platform. Electromyography of four muscles was recorded. Results show that countermovement magnitude and volitional effort both affect jump performance. These effects were synergistic for jump height (P < 0.001), but antagonistic for peak ground reaction force (P < 0.001). Interestingly, peak jump mechanical power was affected by volitional effort, implying an increase from 31.26 W/kg at 25% to 41.68 W/kg at 100% of volitional effort, but no countermovement magnitude effect was observed for 100% of volitional effort. This suggests that the apparent paradox of larger ground reaction forces in sub-maximal as compared to maximal jumps is due to the different jump strategies. Moreover, these results are relevant for jumping mechanography as a clinical tool, suggesting that peak power can be used to assess neuromuscular performance even when countermovement magnitude varies as a result of age or pathology.