The correlation between jump height and mechanical power in a countermovement jump is artificially inflated

The countermovement jump is commonly used to assess an athlete’s neuromuscular capacity. The aim of this study was to identify the mechanism behind the strong correlation between jump height and mechanical power in a countermovement jump. Three athletes each performed between 47 and 60 maximal-effort countermovement jumps on a force platform. For all three athletes, peak mechanical power and average mechanical power were strongly correlated with jump height (r = 0.54–0.90). The correlation between jump height and peak power was largely determined by the correlation between jump height and the velocity at peak power (r = 0.83–0.94) and was not related to the correlation between jump height and the ground reaction force at peak power (r = −0.20–0.18). These results confirm that the strong correlation between jump height and power is an artefact arising from how power is calculated. Power is a compound variable calculated from the product of instantaneous ground reaction force and instantaneous velocity, and application of statistical theory shows that the correlation between jump height and power is artificially inflated by the near-perfect correlation between jump height and the velocity at peak power. Despite this finding, mechanical power might still be useful in assessing the neuromuscular capacity of an athlete.