Effect of Isometric Hip Abduction on Foot and Ankle Muscle Activity and Medial Longitudinal Arch During Short-Foot Exercise in Individuals With Pes Planus

Context: The improvement of hip joint stability can significantly impact knee and rearfoot mechanics. Individuals with pes planus have a weak abductor hallucis (AbdH), and the tibialis anterior (TA) may activate to compensate for this. As yet, no studies have applied isometric hip abduction (IHA) for hip stability during short-foot exercise (SFE). Objective: To compare the effects of H-IA on the muscle activity of the AbdH, TA, peroneus longus (PL), and gluteus medius (Gmed), as well as the medial longitudinal arch (MLA) angle during sitting and standing SFE. Design: Two-way repeated analyses of variance were used to determine the statistical significance of AbdH, TA, PL, and Gmed electromyography activity, as well as the change in MLA angle. Setting: University research laboratory. Participants: Thirty-two participants with pes planus. Intervention(s): The participants performed SFE with and without isometric hip abduction in sitting and standing positions. Main Outcome Measures: Surface electromyography was used to measure the activity of the AbdH, TA, PL, and Gmed muscles, and Image J was used to measure the MLA angle. Results: Significant interactions between exercise type and position were observed in terms of the PL muscle activity and in the change in MLA angle only, while other muscles showed significant main effects. The IHA during SFE significantly increased the AbdH muscle activity, while the TA muscle activity was significantly lower. The muscle activity of Gmed and PL was significantly increased in the standing position compared with sitting, but there was no significant difference with or without IHA. The change in the MLA angle was significantly greater in SFE with IHA in a standing position than in the other SFE conditions. Conclusions: IHA may be an effective method for reducing compensatory TA activity and increasing AbdH muscle activity during SFE for individuals with pes planus.