Lower Extremity Stiffness and Linear Acceleration Performance in Basketball Players: Relationships Between Jump-Derived Stiffness Indices and Sprint Kinematics.

BACKGROUND Lower-extremity stiffness is a key determinant of sprint and jump performance; however, its relationship with acceleration-phase kinematics, including step frequency (SF), step length (SL), and ground contact time (GCT) remains poorly characterized in team sport athletes. This study examined associations between jump-derived stiffness and 10 m sprint kinematics in collegiate basketball players and compared kinematic profiles between faster and slower athletes. MATERIAL AND METHODS Fifteen male collegiate basketball players completed a 10 m sprint (splits: 0-5 m, 5-10 m, 0-10 m) with kinematics captured via dual high-speed cameras (240 fps). Lower-extremity stiffness was assessed using a portable force plate during countermovement jump (CMJ), drop jump (DJ), and hopping. Athletes were stratified by median split. Pearson correlations examined stiffness kinematic relationships within the fast group. RESULTS The fast group demonstrated significantly greater 0-5 m SF (4.16±0.34 vs 3.67±0.39 Hz; P=0.026) and SL (188.18±10.87 vs 167.03±15.71 cm; P=0.010). SF showed near-perfect negative correlations with 0-5 m (r=-0.99) and 0-10 m sprint times (r=-0.99; both P<0.001). CMJ vertical stiffness, hopping knee and ankle stiffness, and DJ knee stiffness yielded large to very large correlations with GCT, SF, and SL, respectively, but were nonsignificant (P>0.05). No between-group stiffness differences were detected. CONCLUSIONS SF was the kinematic variable most strongly associated with early-phase acceleration. Stiffness kinematic correlations, although large in magnitude, failed to reach statistical significance in this small sample. Findings should be considered exploratory; larger longitudinal studies are required before jump-derived stiffness indices can be recommended for performance monitoring.