A comparison of the ground reaction force frequency content during rearfoot and non-rearfoot running patterns.

Running with a non-rearfoot pattern has been claimed to reduce injury risk because the impact peak in the vertical ground reaction force (GRF) is visually absent in the time-domain compared with a rearfoot pattern. However, running results in a rapid deceleration of the lower extremity segments immediately following initial contact with the ground, regardless of footfall pattern. Therefore, the frequency content of the GRF is expected to contain evidence of this collision. The purpose of the present study was to characterize the waveform components of the GRF generated during the impact phase by habitual rearfoot and habitual non-rearfoot pattern groups using the continuous wavelet transform. Twenty rearfoot and 20 non-rearfoot participants ran over-ground at a standardized speed with their habitual footfall pattern. The continuous wavelet transform was performed on the resultant GRF vector and the vertical GRF. GRF signals generated by the non-rearfoot pattern group during early stance had maximum signal power of 15.4±9.1Hz occurring at 23.1±6.3% of stance, which is within the 10-20Hz range previously associated with impact in rearfoot runners. Maximum signal power occurred earlier in the impact phase (11.5±1.5%) and with a higher frequency (27.2±3.9Hz) in the rearfoot pattern group verses the non-rearfoot pattern group (P<0.05). While the impact force transient may not appear as a prominent feature within the time-domain GRF with a non-rearfoot pattern, the results indicate that both footfall patterns generate frequencies associated with the impact peak in the resultant and vertical GRF.