earticle

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Background: Flexible flatfoot is a condition in which the medial longitudinal arch collapses under weight-bearing despite appearing normal at rest. This structural change may result in muscle imbalances and impaired foot function. Short foot exercises (SFE) are often used to strengthen intrinsic foot muscles and improve arch stability. Prior studies have demonstrated that combining hip abduction with SFE enhances abductor hallucis activation and supports medial arch correction. However, the effects of different levels of hip abduction resistance on this mechanism remain unclear. Methods: Twelve adults (mean age 27.92 years) with flexible flatfoot participated. Participants performed SFE under four randomized hip abduction resistance conditions (0㎏, 5㎏, 10㎏, 15㎏). The muscle activity of the abductor hallucis (Abd.H), tibialis anterior (TA), peroneus longus (PL), and gluteus medius (G.med) was measured using Noraxon Ultium surface EMG. Each condition was repeated three times with a one-minute rest between contractions and a three-minute rest between conditions. Data were analyzed using repeated measures ANOVA and LSD post-hoc analysis (α=.05). Results: Abductor hallucis showed a statistically significant increase in muscle activation as resistance increased (p<.001), with the largest increase between 0㎏ and 5㎏. No significant differences were observed among the higher resistance levels. Tibialis anterior activity also significantly increased under the 5㎏ and 10㎏ conditions compared to 0㎏ (p=.023, p=.033). The peroneus longus and gluteus medius showed no significant overall differences, although PL approached significance between 0㎏ and 10㎏ (p=.061), and G. med displayed a quadratic trend (p=.030). Conclusion: Hip abduction resistance during SFE significantly enhances abductor hallucis activity in individuals with flexible flatfoot, especially at 5㎏ resistance. This suggests that minimal resistance can effectively promote intrinsic foot muscle activation, offering a targeted intervention strategy for arch support and rehabilitation.