Metatarsophalangeal joint flexion affects dorsiflexor activity in subjects with a dominant extensor hallucis longus

BACKGROUND AND OBJECTIVES: Normal dorsiflexion (DF) required for normal gait is achieved through balance of the tibialis anterior (TA) and extensor hallucis longus (EHL). Imbalance may induce ankle and foot deformities and exacerbate pathology. EHL dominance is associated with progressive TA weakness, attributable to muscle non-use. When the EHL dominantly dorsiflexes the ankle, the big toe extends at the metatarsophalangeal joint (MTPJ) and pure ankle DF is absent. The effects of active MTPJ flexion on TA and EHL muscles, TA/EHL ratio, and the force applied during active DF in EHL-dominant (EHLD) and EHL-non-dominant (EHL-ND) subjects were compared. METHODS: The 38 subjects were divided into EHL-D and EHL-ND groups. All subjects performed active ankle DF with and without active MTPJ flexion. Surface electromyographic data, ankle active range of motion, and DF force were measured. Two-way mixed analysis of variance was used to evaluate differences in dependent variables. RESULTS: Compared to the EHL-ND group, the EHL-D group exhibited less TA activity, more EHL activity, and a reduced TA/EHL activity ratio. Active application of MTPJ flexion during DF significantly reduced muscle imbalance, whereas EHL activity decreased and the TA/EHL activity ratio increased. The DF force decreased significantly with MTPJ flexion in both groups. CONCLUSIONS: Active MTPJ flexion can reduce EHL and/or increase TA activity and increase the TA/EHL activity ratio during active ankle DF in both EHL-D and EHL-ND subjects.