Directional contrasts in center of pressure and external knee adduction moment during stepping with wedge insoles, verbal instructions, and perceptual plantar cues: An exploratory within-subject study

BACKGROUND: Mediolateral center of pressure (COP) position can influence frontal-plane knee loading, but directional responses to different plantar-guidance approaches remain unclear. RESEARCH QUESTION: How do participant-level contrasts between opposing medial and lateral conditions in COP and external knee adduction moment (KAM) differ across wedge, verbal instruction, and perceptual stimulus insole modes performed in a fixed sequence? METHODS: Twenty-two healthy men performed a stepping task under wedge, verbal instruction (VI), and perceptual stimulus insole (PSI) modes in the fixed order wedge → VI → PSI. Within each mode, medial preceded lateral. Ten trials were recorded per direction, and trials 3-7 were averaged. Directional contrasts were defined as the lateral directional condition minus the medial directional condition. Between-mode comparisons were interpreted descriptively because both orders were fixed. RESULTS: Median ΔCOP values for wedge, VI, and PSI were 0.94, -10.77, and -18.14 mm at the first KAM peak and 0.70, -13.38, and -31.02 mm at the second peak (both omnibus p < 0.001). Wedge differed from VI and PSI, whereas VI and PSI did not differ significantly at either peak. ΔKAM also differed among blocks at both peaks (both p < 0.001), but the pairwise pattern differed: PSI differed from wedge and VI, whereas wedge and VI did not. SIGNIFICANCE: Opposing directional conditions produced measurable participant-level COP and KAM contrasts, but COP and KAM did not show the same pairwise pattern. Because both orders were fixed, these findings are hypothesis-generating and require randomized or counterbalanced testing.