Plantar Intrinsic Foot Muscle Activity Across the Foot Posture Spectrum When Walking in Nontextured and Textured Foot Orthoses.

Abstract

To investigate the magnitude differences of 4 plantar intrinsic foot muscles (PIFMs) across the foot posture spectrum during gait, and to investigate activation differences when adding cutaneous mechanoreceptor stimulation within foot orthosis design. A cross-sectional study. University's biomechanics research laboratory. Thirty-two healthy young adults (27 ± 5.2 years; 18 men, 14 women; 175.5 ± 10.4 cm; 80.2 ± 18.7 kg) participated in this study. Anatomical foot posture variance of participants was characterized from highly pronated to highly supinated using the Foot Posture Index. Participants wore 2 different types of foot orthoses, nontextured orthoses and orthoses with a textured top cover intentional to increase activation of foot sole cutaneous mechanoreceptors, while completing a walking protocol. Ultrasound-guided fine-wine electromyography recorded muscle activity from 4 PIFMs: abductor hallucis, adductor hallucis (transverse head), flexor digitorum brevis, and abductor digiti minimi. Within the same foot posture, walking in textured orthoses significantly increased muscle activity of PIFMs compared with walking in nontextured orthoses. Most noteworthy, walking in foot orthotics modulates plantar foot intrinsic muscle activity, although static foot posture is not an indicator of PIFM activation. This study opens an interesting line of research exploring the link between-foot orthoses design, tactile feedback, and PIFMs activation during gait.