Multi-planar intersegmental coordination differs between retrained and habitual non-rearfoot strikers

Purpose This study aimed to compare multi-planar shank-foot coordination patterns and variability during stance between runners who transitioned from a rearfoot strike (RFS) to a non-rearfoot strike (NRFS) through gait retraining (RETs) and habitual NRFS runners (HABs). Methods Thirty-eight runners (18 RETs, 20 HABs) were analyzed. Multi-planar shank-foot coordination patterns and coordination variability (CV) were quantified across three key couplings using a modified vector coding technique. Sagittal-plane and impact-related outcomes, coordination-pattern proportions, and CV were analyzed using independent-samples tests, Mann-Whitney U tests, and generalized linear mixed models, respectively. Results Primary analyses showed no statistically significant between-group differences in foot-strike angle, peak vGRF, VALR, or VILR. Covariate-adjusted sensitivity analyses identified lower VALR and VILR in RETs ( P = 0.040 and P = 0.025). Coordination-pattern proportions differed during P4 of the shank transverse vs. foot sagittal coupling, with RETs exhibiting greater anti-phase distal-dominant and lower in-phase distal-dominant coordination. Significant group × phase interactions in CV were observed across all three couplings ( P ≤ 0.002), with greater CV in RETs during P2 of the shank frontal vs. foot sagittal coupling ( P = 0.021). Conclusion Phase- and coupling-specific differences in shank-foot coordination were observed between HABs and RETs who completed gait retraining and demonstrated an NRFS pattern at testing. Multi-planar coordination analysis may therefore provide complementary information beyond foot-strike classification and selected sagittal-plane or external loading measures.