Frequency Content of the Vertical Ground Reaction Force Component During Rearfoot and Forefoot Running Patterns

Abstract

The forefoot (FF) footfall pattern has been advocated to reduce running overuse injuries due to the lack of the impact peak in the vertical ground reaction force component (vGRF). Although the vertical impact peak has been associated with running overuse injuries, the frequency content of vGRF may provide more insight into injury mechanisms. Previous studies have found passive mechanisms, such as the deformation of bone and articular cartilage, are responsible for attenuating high frequency signals. Conversely, active mechanisms, such as eccentric muscle contractions and kinematic adjustments, attenuate low frequencies. The lack of the vertical impact peak during FF running may alter the frequency content of the vGRF therefore altering how the body tissues attenuate impact shock. PURPOSE: To determine the frequency content of the vGRF during rearfoot (RF) and FF running. We hypothesize RF running will result in greater amplitudes at higher frequencies whereas FF running will result in greater amplitudes at low frequencies. METHODS: Seven natural RF runners and 7 natural FF runners performed 10 trials over ground with each footfall pattern. Running speed was restricted to ±5% of the subjects preferred speed. GRFs were collected at 1200Hz. vGRFs from the stance phase were zero padded to equal 2048 data points. An FFT was performed on each trial then normalized to 1 Hz bins. A mixed factor ANOVA with subjects nested within footfall pattern was performed to assess differences in amplitude at frequencies 1 - 50 Hz (α = 0.05). RESULTS: RF running resulted in significantly greater amplitudes for frequencies 13 - 39 Hz (p<0.05; sum of amplitudes 13-39 Hz: RF = 462 N; FF = 166 N; percent difference = 94.7%). FF running resulted in significantly greater amplitudes for frequencies ranges 5 - 7 Hz (p<0.05; sum of amplitudes 5-7 Hz: RF = 436 N, FF = 542 N; percent difference = 21.7%). CONCLUSIONS: The frequency content of the vGRF suggests RF running necessitates a greater reliance on passive mechanisms to attenuate impacts whereas FF running relies on active mechanisms. The results suggest there may be a difference in impact related injury mechanisms between running footfall patterns. The RF footfall pattern may contribute to bone related injuries whereas the FF footfall pattern may contribute to injuries such as muscle strain and tendonitis.