Influence of rearfoot and forefoot midsole hardness on biomechanical and perception variables during heel-toe running

Abstract Purpose: Running shoe cushioning research has focused widely on rearfoot (RF) characteristics, whereas forefoot (FF) characteristics have been rather neglected. However, altered cushioning may affect running biomechanics and respective subjective perception at RF and FF. Thus, this research compared the effect of running shoes with different midsole hardnesses at RF and FF. Methods: Twenty-eight heel-toe runners were tested in five experimental shoe conditions that featured three segmented EVA midsoles (RF, midfoot (MF), FF). Three conditions had the same midsole hardness at RF and FF (soft (SS), medium (MM), hard (HH)). Two conditions had different RF and FF midsole hardness (soft-RF/hard-FF (SH), hard-RF/soft-FF (HS)). All midsoles featured the same MF segment of medium hardness. Vertical ground reaction forces and lower extremity kinematics during stance, subjective cushioning of the heel-toe transition and the overall comfort were quantified. Data were analysed using Kolmogorov-Smirnov tests, repeated measures ANOVA, Bonferroni post-hoc tests (p < 0.05), and effect size analyses (pη2). Results: The consistent midsole shoe conditions showed increased maximum loading rates of impact and propulsion peaks from SS to HH. Respective maximum loading rates of SH were similarly to SS, and respective maximum loading rates for HS were similar to HH. Subjectively, the consistent midsole conditions were rated according to their mechanical properties and softer shoes were preferred over harder shoes. In the varied midsole shoe conditions, SH was perceived similar to SS, whereas HS was perceived similar to MM. Conclusion: The examined biomechanical variables were influenced almost entirely by respective RF cushioning properties. The hard FF did not negatively affect cushioning perception as long as the RF was soft. Combining a soft FF with a hard RF improved inferior cushioning perception associated with shoes being hard at RF and FF.