Electromyographic examination of a new exercise therapy for the intrinsic and extrinsic foot muscles.

[Purpose] Flatfoot is a risk factor for running-related injuries. Although short foot exercise (SFE) is commonly used in the treatment of flatfoot and mainly induces the intrinsic foot muscles, it has little effect on foot kinematics. The intrinsic and extrinsic foot muscles are required for maintaining the foot arch; thus, we have developed the arch raise exercise (ARE). [Participants and Methods] Ten feet of 10 participants with flatfoot and 10 feet of 10 healthy participants were included. Muscle activity was measured during ARE, SFE, and heel raise (HR). The muscle activity levels of the abductor hallucis, flexor hallucis brevis, abductor digiti minimis, flexor digitorum longus, peroneus longus, peroneus brevis, and the lateral and medial heads of the gastrocnemius were measured. [Results] In the flatfoot group, ARE generated greater intrinsic and extrinsic muscle activity compared to those generated by the SFE; however, these effects were not significant. In the flatfoot group, the activities of the abductor hallucis and peroneus brevis were greater during the ARE than during HR. [Conclusions] ARE and SFE can generate comparable activity of the intrinsic foot muscles. Compared with SFE, ARE can generate greater activity in the extrinsic muscles.