Slower Walking Speed in Older Men Improves Triceps Surae Force Generation Ability

Abstract

Purpose: Older adults walk slower than young adults but it is not known why. Previous research suggests that ankle plantarflexors may have a crucial role in the reduction of walking speed. The purpose of this study was to investigate age-related differences in triceps surae muscle-tendon function during walking to further investigate the role of plantarflexors in the age-related reduction of walking speed. Methods: Medial gastrocnemius and soleus muscle fascicle lengths were measured using ultrasound imaging during walking from 13 young (25±4yrs) men at preferred walking speed, and from 13 older (73±5yrs) men at preferred speed and at the young men's preferred speed. Muscle-tendon unit lengths were calculated from joint kinematics and tendinous tissue lengths were calculated by subtracting muscle lengths from muscle-tendon unit lengths. In addition, ground reaction forces and electromyographic activity of medial gastrocnemius and soleus were measured. Results: In both medial gastrocnemius and soleus it was observed that at preferred walking speed, older men used a narrower muscle fascicle operating range and lower shortening velocity at the estimated time of triceps surae peak force generation compared to young men. Fascicles also accounted for a lower proportion of muscle-tendon unit length changes during the stance phase in older compared to young men. Significant differences in triceps surae muscle function were not observed between age groups when compared at matched walking speed. Conclusions: In older men, walking at preferred speed allows triceps surae muscles to generate force with more favorable shortening velocity and to enhance use of tendinous tissue elasticity compared to walking at young men's preferred speed. The results suggest that older men may prefer slower walking speeds to compensate for decreased plantarflexor strength.

Achilles tendon stiffness minimizes the energy cost in simulations of walking in older but not in young adults

“…This is in contrast with a previous study suggesting that increasing Achilles tendon stiffness would decrease the energy cost of walking in older adults based on an independent correlation between Achilles tendon stiffness and maximal walking capacity measured using the six-minute walk distance (Stenroth et al, 2015). However, this study did not take into account the influence of age-related differences in walking patterns on triceps surae muscle contractile conditions (Stenroth et al, 2016).…”

Ultrasound imaging links soleus muscle neuromechanics and energetics during human walking with elastic ankle exoskeletons

“…Given the non-linear curvature of muscle's F-L relationship, a given shift in muscle length could induce a larger improvement in economy when starting from even shorter lengths. For example, Achilles tendon compliance increases with advanced aging 73 , stroke 74 or paralysis 75 and this likely shifts the plantar flexor muscles to shorter operating lengths and faster shortening velocities, conditions that increase metabolic rate 76,77 . Furthermore, in cases where the foot-ankle complex becomes stiffer (e.g., diabetic neuropathy 78 ), intervening by adding stiffness to the foot instead of the ankle joint may improve plantar flexor capacity by yielding slower, more economical shortening velocities.…”

Ultrasound imaging links soleus muscle neuromechanics and energetics during human walking with elastic ankle exoskeletons

“…Given the non-linear curvature of muscle’s F-L relationship, a given shift in muscle length could induce a larger improvement in economy when starting from even shorter lengths. For example, Achilles tendon compliance increases with advanced aging 73 , stroke 74 or paralysis 75 and this likely shifts the plantar flexor muscles to shorter operating lengths and faster shortening velocities, conditions that increase metabolic rate 76,77 . Furthermore, in cases where the foot-ankle complex becomes stiffer ( e.g.…”