The impact of changing running technique on lower limb nonlinear dynamics in recreational runners

This study aims to investigate the impact of changing running techniques on lower limb variability, regularity/ complexity, and long-range correlations. Twelve healthy male recreational runners performed treadmill running at 3 m/s and 4 m/s. After a 5-min familiarization, baseline data were collected. A 16-camera motion capture system recorded joint angles of the right knee and ankle. Five minutes of steady-state data per condition were analyzed. Variability was quantified using the coefficient of variation; regularity/complexity and long-range dependence were quantified using SampEn and DFA-α (knee and ankle; sagittal, coronal, transverse planes). Two-way ANOVA (speed × training) tested main and interaction effects. After changing, increased stride length and reduced vertical ground reaction force (p < 0.05), while CV of lower-limb kinematics did not change significantly. DFA-α increased in the transverse plane for the knee and ankle (Training main effects, p < 0.05). A significant Speed × Training interaction was observed for knee coronal DFA-α: α increased at 3 m/s but decreased at 4 m/s (p < 0.05). SampEn showed speed-related effects in the sagittal plane. Changing running techniques did not change variability magnitude but altered nonlinear dynamics, particularly by increasing long-range correlations in the transverse plane and producing speed-dependent effects in the coronal plane. This pattern suggests an adaptive redistribution of control across planes and between proximal and distal joints as running speed increases.