Effects of altering plantar flexion resistance of an ankle-foot orthosis on muscle force and kinematics during gait training.

Ankle-foot orthosis (AFO) can improve gait in stroke patients. Addition of plantar flexion resistance (PFR) can improve the first foot rocker function. However, the effect of changing the PFR on the ankle muscle force during gait training is unclear. This study aimed to determine the effect of changing the PFR of an AFO on spatiotemporal parameters (speed, bilateral step length, and cadence), peak angle of ankle plantar flexion and knee flexion, and muscle force (tibialis anterior [TA], medial head of the gastrocnemius [MGAS], and soleus) during early stance using a musculoskeletal model. Ten healthy adult men walked under five conditions: a no-AFO condition and PFR conditions 1-4. Spatiotemporal parameters and peak joint angles during the early stance phase were measured from experimental data, with muscle force estimated from simulations of a musculoskeletal model. Increasing the PFR of the AFO decreased TA muscle force and increased MGAS muscle force but had no influence on spatiotemporal parameters and joint angles. Adjustment of the PFR modifies the muscle force around the ankle, which can maximize the effect of AFO during gait training.