Variability of the impact transient during repeated barefoot walking trials

Most studies of human gait assume that the normal gait patterns are consistent and therefore that it is adequate to assess the baseline condition once. However, recent research has brought this assumption into question. The purpose of this study is to evaluate the repeatability of components of the ground reaction force, peak force loading rate and percent of ground reaction force at impact above 60 Hz, across repeated walking trials throughout the experiment. Twenty-two subjects walked barefoot 10 times across a force platform interspersed between trial blocks of three different shod conditions. We used traditional grouped data analysis (ANOVA) as well as a more novel single-subject analysis. The grouped analysis revealed one statistically significant comparison between barefoot trials for the root mean square greater than 60 Hz variable. The single-subject analysis revealed that approximately 5% of the barefoot trials were significantly different for each of the peak force loading rate and percent of impact transient signal above 60 Hz variables. We suggest that these results, from both data analysis techniques, are not biologically relevant because the magnitudes of most of the changes were not large enough to have a biological significance (peak force loading rate differences less than 50%, and less than 0.05-fold differences in the percent of the ground reaction force above 60 Hz). In conclusion, our data suggest that baseline impact force measurements during walking are stable and do not need to be recorded between experimental conditions in walking studies.