Vertical jump performance is affected by the velocity and depth of the countermovement.

This study aimed to explore the effect of the velocity and depth of the countermovement on vertical jump performance and the shape of the force-time curve. Seventeen university students performed two blocks of 18 countermovement jumps (CMJ) being instructed to jump for maximum height after performing the countermovement at a self-selected (SS-CMJ) or fast (F-CMJ) velocity. Each block consisted of six CMJ from a larger depth, six CMJ from a shorter depth, and six CMJ from a self-preferred depth. Mean and peak values of force, velocity and power, reactive strength index-modified (RSImod), jump height, and the shape of the force-time curve (unimodal or bimodal) were assessed. The F-CMJ provided a higher (mean and peak force, mean velocity, mean power, and RSImod) or comparable (peak power, peak velocity, and jump height) performance than the SS-CMJ. The shorter CMJ provided the highest values of mean and peak force, mean and peak power, and RSImod, while peak velocity and jump height were higher for the larger and self-preferred CMJ. The force-time curve was bimodal during the larger CMJ (100%) and unimodal during the shorter CMJ (65-88%). These results highlight that CMJ performance is influenced by the velocity and depth of the countermovement.