Influence Of Foot Posture On Ground Reaction Forces

Abstract

Most running injuries are related to compounded stresses that occur at the lower extremities (LE). Previous literature has indicated runners with extremes in arch height (pes planus or pes cavus) are more susceptible to injuries than those with average arch structure. Although the relationship of LE stress and injury is well documented, little research describing attenuation of vertical ground reaction forces (vGRF) related to arch height exists in the current literature. PURPOSE: To examine the relationship between vGRF and the change in arch height in load bearing conditions, during running bouts. METHODS: Eighteen healthy female college aged Division I cross country runners (mean age = 20 ± 1.7 yrs; ht = 164.4 cm ± 6.7 wt = 54.4 kg ± 5.4) participated in 5 - 7 running trials on a force plate (AMTI, OR-6, Watertown, MA) instrumented runway sampling vGRF data in body weights (BW) at 960 Hz. Measurement of navicular height and truncated foot length were taken in non-weight bearing (NWB) and weight bearing (WB) conditions prior to the running bouts to determine the calculated arch index (CAI). CAI was compared to vGRF using pearson's correlation (SPSS, IL; a=.05). Linear regression was constructed to predict peak vGRF based on CAI (a=.05). Participants were also surveyed regarding history of LE pain and injury. RESULTS: A significant negative correlation (-.567, p=.012) was reported when comparing CAI to vGRF. Linear regression indicated 33.2% of the variance observed in vGRF was explained by the decrease in CAI in the NWB and WB conditions. CONCLUSIONS: The comparative negative correlation between CAI and vGRF indicates that individuals with a greater residual arch height in the NWB and WB conditions (greater CAI) tend to exhibit lower vGRF during self paced running bouts. Anecdotally, those with low CAI, with less than 10% change in NWB to WB arch height, tended to have history of knee pain. These individuals also exhibited the highest amount of vGRF during running bouts. These data indicate that the calculation of CAI may predict a runner's ability to attenuate vGRF and lend insight into causation of LE injury.