Influence of toe flexor muscle fatigue on stiffness of the intrinsic foot muscles

BACKGROUND: Assessing intrinsic foot muscles (IFM) is important for understanding their role in loading movements. Additionally, knowledge of the impact of IFM following toe flexor muscle fatigue may aid the teaching of IFM exercises. OBJECTIVE: To examine the influence of toe flexor muscle fatigueon IFM stiffness using ultrasound shear-wave elastography. METHODS: This study included 19 college students. IFM stiffness at 10%, 50%, and 90% body weight was measured using ultrasound-based shear-wave elastography. IFM including the abductor hallucis (AbH), flexor hallucis brevis (FHB), flexor digitorum brevis (FDB), and quadratus plantae (QP) were assessed. The fatigue induction protocol comprised a series of toe flexions at a controlled pace of 40 beats per minute and an amplitude of 75% of the maximum toe flexor strength for a duration of 5 minutes. RESULTS: Muscle stiffness significantly increased with increasing load. Toe flexor muscle fatigue significantly increased the stiffness of the FDB. CONCLUSIONS: IFM stiffness significantly increased with increasing load, and the stiffness of FDB significantly increased in the toe flexor muscle fatigue condition at DLS and SLS loads. The findings of this study will contribute to the study and clinical setting of IFM exercises.