Biomechanical and Energetic Consequences of Stride Length–Frequency Modulation across Running Speeds

Abstract

Running speed is governed by coordinated adaptations in stride mechanics and center-of-mass (CoM) dynamics, and this study examined speed-dependent changes in stride parameters, CoM kinematics, and mechanical energy during slow and fast running using two-dimensional kinematic approach and computational modeling. A physically trained adult performed self-selected slow and fast running trials, with hip marker trajectories used as a surrogate for CoM motion. Slow running was characterized by a lower stride frequency (≈ 0.8 Hz), larger vertical CoM displacement (≈ 0.20 m), and greater gravitational potential energy fluctuations (≈ 140 J), accompanied by modest vertical velocity peaks (≈ 0.9 m/s upward and −0.5 m/s downward), indicating lower propulsive and impact demands. In contrast, fast running exhibited a substantially higher stride frequency (≈ 2.67 Hz), reduced vertical CoM oscillation (≈ 0.10 m), and smaller potential energy fluctuations (≈ 70 J), while vertical velocity magnitudes increased markedly (≈ 1.2 to 1.3 m/s upward and −1.1 m/s downward), reflecting elevated mechanical power output and greater impact loading. Total mechanical energy profiles further demonstrated smoother, lower-amplitude fluctuations during slow running and larger, more variable kinetic energy peaks during fast running, consistent with increased reliance on elastic energy storage and return at higher speeds. Collectively, these findings indicate a speed-dependent transition from an economical, low-impact gait strategy at slower speeds to a spring-mass-dominated, high-power locomotor pattern at faster speeds, highlighting the dynamic interplay between stride length, stride frequency, and CoM energy regulation in human running.