Sex differences in soleus strength may predispose middle age women to falls

This study investigated middle age healthy adults to elucidate if plantar flexion (PF) strength differences exist because of the triceps surae or the soleus when comparing between sexes. A random population sample was stratified by sex and included 25 healthy (12 women and 13 men) subjects who volunteered for participation. Dorsiflexion range of motion was measured using a biplane goniometer. Self-reported function was assessed using the Foot and Ankle Ability Measure. Ankle PF strength was assessed using the Biodex System 3. To determine triceps surae vs. soleus strength, testing positions included (1) full ankle dorsiflexion with the knee in full extension and (2) full ankle dorsiflexion with 90° of knee flexion. Results indicated that women were significantly weaker than men in absolute PF strength for both triceps surae and soleus testing positions. Furthermore, even with normalizing PF strength to body mass PF strength deficits persisted. Additionally, when the contribution of the soleus was accounted for in the full knee extended position (triceps surae), normalized strength differences no longer existed between sexes. Therefore, these results indicate that what appeared as triceps surae complex strength deficits in middle age women compared with men was actually soleus weakness. This may suggest that middle age women are predisposed to increased falls at an early age than previously reported. Additionally, this may indicate that the soleus muscle should be a focus of strength training for women during middle age.