flexor substitution

flexor substitution

; FSu ankle joint plantarflexion during heel lift phase of gait, due to action of flexors hallucis and digitorum longus (FHL and FDL) on the ankle joint, in a limb with weak or ineffective gastrocnemius and soleus action; FSu causes clawing of lesser toes at heel lift as FDL and FHL cannot achieve any degree of effective ankle plantarflexion until toes are relatively plantarflexed against the ground surface