Effects of Reduced Achilles Subtendons Relative Displacement on Healthy Elderly Walking: A Simulation Study

Walking in healthy elderly people is characterized by lower performance. Since conventional training programs have had limited success in improving gait performance, it is essential to identify underlying causes of walking deficits in healthy elderly adults. Recent studies have qualitatively shown that the decreased relative displacement of Achilles subtendons is likely the primary contributor to lower propulsion in the elderlys walking by creating a higher dependency on their triceps-surae muscle functions. Due to the invasive nature of experimental investigations, in this study, we developed a computational model and analyzed the effects of reduced Achilles subtendons relative displacement on the total metabolic rate and muscles force profiles during normal walking. Our musculoskeletal simulations revealed a 17% increase in the total metabolic rate in elderly adults whose Achilles subtendons were restricted to have no relative displacement. Changing the restriction level resulted in significant changes in the force distribution of the plantar flexor muscles, notably, a 40% reduction in the Medial Gastrocnemius and a 124% increase in the Soleus forces during the propulsion phase of walking. Also, we quantitatively presented the higher dependency of triceps-surae muscle functions regarding the limitation on their corresponding Achilles subtendons relative displacement. The results of this study confirm the experimental observations and can be used as initial insight into devising novel rehabilitation training programs with the focus on improving Achilles subtendons relative displacement.