Muscular strength plays a crucial role in sports performance and is often evaluated using vertical jump tests such as the Squat Jump (SJ) and Countermovement Jump (CMJ). Measurements based on flight time (FT) assume that takeoff and landing postures are identical, yet differences in ankle position can introduce systematic errors. This study examined whether dorsiflexion (DF) or plantarflexion (PF) of the ankle during the flight phase affects jump height. Forty-three active university students completed four repetitions each of SJ and CMJ under DF and PF across two sessions. Jump heights were recorded using a Chronojump-Boscosystem platform. No significant difference was observed in SJ between DF and PF, while CMJ heights were consistently higher under DF (DF: 28.29 cm ± 7.7 cm vs. PF: 27.08 cm ± 7.03 cm, p = 0.001; d = 0.16). Notably, the effect of DF appeared more pronounced in CMJ, suggesting that higher jumps are more sensitive to postural variations. These findings could suggest that DF can artificially increase jump heights as measured on a jump platform, without reflecting true improvements in force production. Coaches and practitioners should interpret FT-derived data with caution, particularly for higher jumps. Future research combining precise motion capture with force platforms could directly track center-of-mass changes and validate this mechanism.
Ventura et al. (Mon,) studied this question.