THE EFFECT OF STRIDE PERIOD ON THE VERTICAL GROUND REACTIONFORCE DURING WALKING

Abstract

1916 At self selected walking speeds, humans naturally employ a stride period consistent with the resonant period predicted by a modified force driven harmonic oscillator (FDHO) model. Metabolic cost is also minimized at self selected walking speeds, thus resonance has been suggested as the mechanism responsible for the self-optimization of gait. It is unclear whether other performance advantages accompany the use of this biomechanical strategy, such as minimization of ground reaction force loads. The purpose of this study was to determine the relationship between stride period and the vertical ground reaction force (VGRF) during locomotion. It was hypothesized that the first active vertical peak force (F1) would be minimized at the FDHO predicted stride period. Fourteen subjects (73.9 kg, 1.7 m, 28.4 y) were required to walk at a constant treadmill velocity during four stride period conditions: preferred, FDHO predicted and ± 15% of predicted. Stride period and the VGRF data were collected (1200 Hz) from a Gaitway treadmill equipped with two Kistler force plates. A paired t-test (p<0.05) was used to contrast preferred and predicted stride periods. A repeated measures ANOVA (p<0.05) and a trend analysis were implemented to investigate the effect of stride period on the F1 VGRF data. TableTableNo differences were found between preferred and predicted stride periods. The F1 VGRF demonstrated a significant quadratic (U-shaped) curve with a minimum at the predicted stride period condition. Post-hoc pairwise comparisons (Bonferroni) of the F1 VGRF revealed a significant difference between predicted and - 15% stride period conditions. Collectively, these data indicate that individuals optimize the F1 VGRF when they naturally adopt a stride period predicted by a modified FDHO model.