Effects of In-Shoe Midsole Cushioning on Leg Muscle Balance and Co-Contraction with Increased Heel Height During Walking

Abstract

Background: The midsole is an essential assembly of footwear for retaining the shape of the shoe, delivering support to the foot, and serving as a cushioning and stability device for walking. To improve leg muscle balance and muscle co-contraction, we propose a new midsole design for high heels with different hardness levels at the forefoot region. Methods: Five healthy women participated in the study, with a mean ± SD age of 21.80 ± 4.09 years, and duration of high-heeled shoe wear of 5.20 ± 4.09 years. Two midsole conditions, control and multiple-hardness midsole (MHM), with heel heights of 2 (flat), 5, and 8 cm were used. The main outcome measures were to examine the acute effects of MHM by electromyography on muscle activity balance and co-contraction at varying heel heights during shuttle walk. Results: Use of the MHM significantly reduced the muscle activity ratio between the medial and lateral gastrocnemius muscles (P = .043) during push-off to heel strike with a heel height of 5 cm (−22.74%) and heel strike to midstance with a heel height of 8 cm (−22.26%). The increased co-contraction indices of the tibialis anterior–peroneus longus muscles (14.35% with an 8-cm heel height) and tibialis anterior–soleus muscles (15.18% with a 5-cm heel height) are significant (P = .043), with a large effect size (d = 0.8). Conclusions: These results deliver important implications in advancing the engineering of MHM design without changing the in-shoe volume to enhance leg muscle balance and co-contraction during walking.