Effects of Repeated Toe-Flexor Contractions on Hallux Strength and Running Biomechanics in Recreationally Active Adults

Foot muscles contribute to impact attenuation and propulsion during running, yet the effects of repeated toe-flexor contractions and associated strength loss on running biomechanics remain poorly understood. The primary objective of this randomized crossover study was to investigate the acute effects of repeated concentric and isometric toe-flexor contractions on hallux flexion strength, used as an index of fatigue; secondary analyses examined running ground-reaction-force outcomes. Nineteen recreationally active adults completed two interventions one week apart: concentric toe-flexor contractions and isometric toe-flexor contractions combined with electrical stimulation of the medial longitudinal arch. Hallux flexion strength and ground reaction forces during treadmill running at 9 and 12 km·h−1 were assessed before and after each intervention. The concentric protocol reduced hallux flexion strength by 20%, whereas the isometric protocol did not. None of the hypothesis-driven running biomechanical outcomes, including contact duration, impact peak force, active peak force, and vertical stiffness, changed significantly after either protocol. Exploratory secondary analyses suggested changes in selected leg stiffness and impulse variables. In recreationally active adults, repeated concentric toe-flexor contractions induced measurable neuromuscular fatigue, whereas the isometric protocol did not significantly reduce hallux flexion strength; biomechanical changes were limited to exploratory outcomes.