The Effect of Increasing Age on the Concentric and Eccentric Contractile Properties of Isolated Mouse Soleus and Extensor Digitorum Longus Muscles

There is currently a limited amount of literature investigating the age-related changes in eccentric muscle function in vitro. The present study uniquely uses the work loop (WL) technique, to better replicate in vivo muscle function, in the assessment of the age- and muscle-specific changes in acute and sustained concentric and eccentric power and recovery. Whole soleus or extensor digitorum longus (EDL) muscles were isolated from 10-week and 78-week-old mice and acute and sustained concentric and eccentric WL power assessed. Despite an age-related increase in body and muscle mass, peak absolute power for both muscles was unaffected by age. Peak concentric power normalized to muscle mass declined significantly for each muscle, while peak normalized eccentric power declined only for soleus. Fatigue resistance and recovery for the soleus did not differ between age or contraction type. Older EDL was less resistant to concentric fatigue, but was better able to withstand sustained eccentric activity than young EDL. We have shown that age-related changes in muscle quality are more limited for eccentric function than concentric function. A greater bodily inertia is likely to further reduce in vivo locomotor performance in older animals.