Purpose:
Arch-support insoles are widely used in the management of foot postural abnormalities. Therefore, the purpose of this study was to investigate the effect of arch-support insoles on the frequency spectrum of ground reaction forces (GRFs) during running in individuals with anterior cruciate ligament reconstruction (ACLR) and pronated feet.
Methods:
This study employed a quasi-experimental laboratory design. Participants were assigned to four groups: (A) ACLR with pronated feet (6 ± 1 months post-surgery), (B) ACLR with pronated feet (12 ± 1 months post-surgery), (C) ACLR with pronated feet (18 ± 1 months post-surgery), and (D) healthy controls. The frequency spectrum of GRFs was measured using a Bertec force plate (USA). Data were analyzed using two-way repeated-measures ANOVA with a significance level set at p < 0.05.
Results:
The findings demonstrated a significant main effect of the insole condition from pre-test to post-test on the number of necessary harmonics in the vertical direction (control shoe: p = 0.048, η² = 0.20; arch-support insole: p = 0.014, η² = 0.20), mediolateral direction (arch-support insole: p = 0.024, η² = 0.10), and anteroposterior direction (arch-support insole: p = 0.045, η² = 0.10). Additionally, the insole condition showed a significant reduction in the 99.5% power frequency in all three GRF directions under the arch-support insole condition (p < 0.05). Furthermore, a significant insole × group interaction effect was observed in all three GRF directions for the number of necessary harmonics under the arch-support insole condition (p < 0.05).
Conclusion:
The use of arch-support insoles in individuals with ACLR and pronated feet was associated with a reduction in the 99.5% power frequency and an increase in the number of necessary harmonics in the GRF signal during running. These findings suggest that arch-support insoles may alter the time–frequency characteristics of the GRF signal and potentially reduce higher-frequency force components. However, these frequency-domain measures alone do not allow definitive conclusions regarding underlying neuromuscular mechanisms. Further studies are required to clarify the mechanisms underlying these effects.