Manipulating Trunk and Whole Body Posture during Running Influences Ground Reaction Forces

Abstract

Large vertical ground reaction (vGRF) and braking forces have been cited as possible contributors to lower extremity overuse injuries in runners. It is unknown whether these variables can be altered via running form manipulations to decrease injury risk. PURPOSE: To determine if altering trunk and whole body posture during running leads to differences in peak vGRF and peak braking and propulsive forces. METHODS: Fourteen males and fifteen females (age 26.2±0.25 years, height 1.7±0.32 m, weight 67.7±0.37 kg) who were healthy, active, and pain/injury-free volunteered. Participants ran at a self-selected speed across a 15m runway under three conditions: normal self-selected running form (NR), increased trunk flexion (TF), and whole body inclination (WBI). Participants were instructed to bend at the hips (TF) and to lean forward over the ankles (WBI). Five successful trials for each condition were recorded using 3D motion capture and an AMTI force platform. Data was analyzed via 1-way repeated measures ANOVA with Sidak pairwise comparisons for each dependent variable. Statistical significance was set at p<0.05. RESULTS: A significant main effects were found for peak vGRF (p=0.05) and a trend was found for peak propulsive forces (p=0.056). Peak vGRF was significantly less in the TF condition (22.44±2.17 N/kg) than in the NR (22.98±2.01 N/kg, p=0.01) or WBI (22.91±2.55 N/kg, p=0.04) conditions. Max propulsive force was significantly greater for WBI (2.65±0.47 N/kg) than TF (2.54±2.55 N/kg, p=0.006), but there was no significant difference between WBI and NR (p=0.943). There were no significant differences in peak braking forces between conditions (p=0.119). CONCLUSIONS: WBI during running may reduce energy expenditure via anterior displacement of the center of mass relative to the pelvis, resulting in increased propulsive forces. Running with increased TF may reduce injury risk by decreasing peak vGRF. Future studies training TF and/or WBI seem warranted as a form of running gait retraining.