ABSTRACT
BACKGROUND: Previous investigators have shown that high heels decrease the muscle activity of the gastrocnemius muscle during gait. However, it is not known whether commonly used in-shoe heel lifts of lower heights will demonstrate similar effects on muscle activity. The aim of this study was to determine whether heel lifts alter the muscle activity of the ankle plantarflexors and dorsiflexors during the stance phase of gait among individuals with limited gastrocnemius extensibility. MATERIALS AND METHODS: This study used a repeated measures design. Twenty-four healthy volunteers (12 males and 12 females) with less than 5 degrees of passive ankle dorsiflexion with the knee extended participated in the study. Electromyography (EMG), computerized motion analysis, and a force plate were used to measure mean muscle activity of the lateral gastrocnemius, medial gastrocnemius, soleus and tibialis anterior muscles during the stance phase of gait across three walking conditions. Muscle activity was measured as participants ambulated at a self-selected speed in athletic shoes alone and with heel lifts of 6 mm and 9 mm inserted in athletic shoes. RESULTS: Between heel-strike and heel-off, the mean EMG amplitude of the medial gastrocnemius increased with both 6 and 9 mm heel lifts and the amplitude of the tibialis anterior increased with 9 mm heel lifts compared to shoes alone. Between heel-strike and heel-off, there were no significant differences in mean EMG amplitude of the lateral gastrocnemius or soleus muscles walking in heel lifts compared to shoes alone. Between heel-off and toe-off, there were no significant differences in mean EMG amplitude of the lateral gastrocnemius, medial gastrocnemius, soleus, or tibialis anterior muscles when walking in heel lifts compared to shoes alone. CONCLUSION: Heel lifts increase muscle activity of the medial gastrocnemius and tibialis anterior muscles between heel-strike and heel-off among individuals with limited gastrocnemius extensibility. CLINICAL RELEVANCE: We were unable to confirm a decrease in muscle activity when using heel lifts.