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/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.