Electromyographic studies of the human foot: experimental approaches to hominid evolution

Theories about the functions of the foot muscles have centered on their role in arch support. Previous anatomical and electromyographic studies (reviewed herein) have demonstrated that the arches are normally maintained by bones and ligaments. This study reports an electromyographic investigation of five foot muscles (flexor digitorum longus, flexor digitorum brevis, flexor accessorius, abductor hallucis, and abductor digiti quinti) conducted on four humans. The three toe flexors act together to resist extension of the toes during the stance phase of locomotion. Despite the large flexor accessorius in humans, neither this muscle nor the flexor digitorum brevis are preferentially recruited over the flexor digitorum longus for any normal posture or locomotion. The abductors affect the mediolateral distribution of pressure by positioning the forefoot. We suggest that the foot muscles play an important role in positioning of the forces on the foot in both posture and locomotion. Future electromyographic experiments on human and ape foot muscles in conjunction with detailed studies of early hominid fossils promise to elucidate the pathways of human locomotor evolution.