Foot-Strike Adaptations to Step Rate Manipulation: Contrasting Responses of Rearfoot and Midfoot Strike Runners

Step rate (SR) manipulation is a common gait-retraining strategy, but adaptations may vary with baseline foot-strike pattern (FSP). This study examined whether SR manipulation differentially alters FSP in rearfoot strike (RFS) and midfoot strike (MFS) runners. Twenty healthy recreational runners were classified as RFS (n=10) or MFS (n=10) from their preferred running condition. Participants ran at a self-selected treadmill speed under five SR conditions: preferred (PF), -10%, -5%, +5%, and +10%. High-speed video captured left-foot contacts, and the strike index (SI) was calculated to quantify FSP across SR conditions. A two-way mixed-design ANOVA (SR Condition by Group) tested SI differences, followed by Bonferroni-adjusted pairwise comparisons and one-way repeated-measures ANOVAs within each group. The two-way mixed-design ANOVA showed significant effects of SR Condition (p<.001, η²p=.79), Group (p<.001, η²p=.62), and their interaction (p=.03, η²p=.18). Within-group analyses were significant for both RFS (p<.001, η²p=.88) and MFS (p<.001, η²p=.74). In the RFS group, SI was greater at -10% than -5% (p<.001) but did not differ from PF (p=.16). Both +5% and +10% exceeded -10%, -5%, and PF (p<.05), whereas no difference was observed between +5% and +10% (p=.09). In the MFS group, SI was greater at +5% and +10% than at -10%, -5%, and PF (p<.05), whereas no differences were found among -10%, -5%, and PF (p>.999) or between +5% and +10% (p=.27). SR manipulation shifts SI anteriorly in recreational runners, but adaptation depends on baseline FSP. Both groups showed anterior shifts with SR increases that plateaued between +5% and +10%. MFS runners were insensitive to SR reductions, while RFS runners showed more variable responses at lower SRs. SR-based interventions may benefit from stratifying runners by FSP.