Orthoses are often used for the treatment or prevention of injuries. The effect of orthoses on the activity of calf muscles such as the tibialis posterior (TP), flexor digitorum longus (FDL), and peroneus longus (PL) during running is unclear. The purpose of this study was to measure the muscle activity alteration of the TP, FDL, and PL when running with orthoses. Sixteen healthy men participated in this study. Fine-wire and surface electromyography (EMG) were used to measure the TP, FDL, and PL. Participants ran in three conditions: barefoot, footwear only, and footwear with orthoses. The EMG data of the muscles were measured in three successful running trials in each condition. Then, the EMG data from the stance phase of each running trial were used for analysis. The stance phase was further divided into the contact and propulsion phases based on the force plate data. Data from eight participants were used for final analysis because the EMG measurements were unsuccessful for the other eight. The results showed that the TP EMG activity significantly decreased in the orthosis condition in comparison to that in the barefoot condition in all phases. There were no significant differences between barefoot and footwear and footwear and orthosis conditions. No significant changes in the FDL and PL EMG activities were detected in any phase for any of the three conditions. Orthotic use reduces the TP EMG activity level while running, and this result may be beneficial for patients with injuries related to TP overactivity.
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