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The purpose of this study was to investigate the operating length and velocity of the human vastus lateralis (VL) fascicles regarding force and power generation during vertical jumping in vivo. Compared to the SJ, the VL fascicles operated on a more favourable portion of the force-length curve and more disadvantageous portion of the force-velocity curve in the CMJ, indicating a reciprocal effect of force-length and forcevelocity potentials for force generation. The mean fascicle shortening velocity in the CMJ was closer to the plateau of the power-velocity curve, which resulted in a greater powervelocity potential. We provided for the first time evidence for a cumulative effect of three different mechanisms - i.e. greater force-length potential, greater power-velocity potential and greater muscle activity - for an advantaged power production in the CMJ.