Evaluation of the activities of the intrinsic and extrinsic muscles of the foot during toe flexion with or without interphalangeal joint flexion using ultrasound shear wave elastography.

The intrinsic muscles of the foot are important to maintain the arch of the foot and to participate in sports activities. Using ultrasound shear wave elastography, we investigated the effect of different toe flexion methods on the activity of the intrinsic and extrinsic muscles of the foot. The study included 15 healthy adults who performed toe flexion under 2 conditions: with interphalangeal (IP) joint flexion and without IP joint flexion. The applied load during flexion was 500 g. Muscle stiffness was measured in the abductor hallucis, flexor hallucis brevis, flexor digitorum brevis, quadratus plantae, flexor hallucis longus, and flexor digitorum longus muscles using ultrasound shear wave elastography. Muscle stiffness was statistically compared with IP flexion and without IP flexion (P < 0.05). The stiffness of the abductor hallucis (P < 0.0005), flexor hallucis brevis (P = 0.022), and flexor digitorum brevis muscles (P < 0.0005) was significantly greater without IP flexion than with IP flexion. In contrast, the muscle stiffness of the flexor hallucis longus (P = 0.001) and the flexor digitorum longus (P = 0.004) was significantly greater during with IP flexion than without IP flexion. This study shows that the abductor hallucis, flexor hallucis brevis, flexor digitorum brevis muscles are more active during toe flexion without IP flexion. These results suggest that the toe flexion method is important for more effective training of the intrinsic muscles of the foot.