Differences in vertical ground reaction forces during first attempt of barefoot running in habitual shod runners

Many suggest that switching from shod running to barefoot running decreases injury risk and makes running more natural. Scientists have reported biomechanical differences in shod and barefoot running, with a number of differences related to increased injury risk. Our research is focused on investigating the acute differences when switching to barefoot running for the first time. Twenty long distance runners were subjected to an experiment as part of this research. The subjects ran 5 trials across two force plates both in shod and barefoot conditions. The ground reaction force (GRF) was recorded for each subject. The stance time, the initial impact loading rate (LR), the impact maximum (IM), the time when the IM was reached, the thrust maximum, the average vertical GRF, and the decay rate (DR) were calculated from the obtained GRF. The results show that the mean LR and DR were greater by 42.191 BW/s (p=0.006) and 5.922 BW/s (p<0.001) respectively in barefoot running compared to shod running. The mean stance time and the time to IM was greater by 10.15 ms (p=0.013) and 5.00 ms (p=0.017) respectively in shod running compared to barefoot running. IM and LR had a significant correlation in shod running condition only (r=0.842, p<0.001). Both conditions, however, had significant correlation between LR and time to IM (shod: r=-0.646, p=0.002; Bare: r=-0.741, p<0.001). According to our data, the responses of the subjects to barefoot running were not unambiguous and in some cases not less traumatic.