Lower-Extremity Joint Function During a Drop Jump: Relationships to Performance and Maximal Strength

ABSTRACT: Haischer, MH, Ahn, N, and Kipp, K. Lower-extremity joint function during a drop jump: relationships to performance and maximal strength. J Strength Cond Res XX(X): 000-000, 2026-Humans modulate joint stiffness during movement based on stretch-shortening cycle (SSC) loading demands. In performance tasks such as jumping, the SSC helps maximize vertical impulse through potentiation of concentric force after eccentric loading. However, joints can serve different locomotor functions (i.e., strut, spring, motor, or damper) while coordinating to achieve an overarching goal. Furthermore, while strength may benefit the ability to regulate joint stiffness under load, what joint functions facilitate optimal SSC task performance and their relationship to maximal strength is not well-understood. The purpose of this study was to describe lower-extremity joint function during a drop jump and characterize the associations to performance outcomes (jump height, ground contact time [GCT], and reactive strength index [RSI]) and relationships to maximal strength. Forty-five collegiate or club level athletes performed drop jumps off a 12-inch box while motion capture and ground reaction force data were recorded. Stance phase kinematics and kinetics were used to calculate joint functional indices (JFI) for the ankle, knee, and hip, reported as relative percentages of strut-, spring-, damper-, and motor-like mechanical behavior. Peak force from an isometric midthigh pull was also recorded as a proxy for strength, and correlations and elastic net regression analyses were performed (p ≤ 0.05). Strut, spring, motor, and damper was the rank order of JFI at all joints. Stronger athletes exhibited greater knee motor function, which was associated with a shorter GCT, greater jump height, and better RSI. Greater relative strength positively influences jump performance by enhancing the ability to generate mechanical energy.