The effects of 8 weeks voluntary wheel running on the contractile performance of isolated locomotory (soleus) and respiratory (diaphragm) skeletal muscle during early ageing.

Decreased skeletal muscle performance with increasing age is strongly associated with reduced mobility and quality of life. Increased physical activity is a widely prescribed method of reducing the detrimental effects of ageing on skeletal muscle contractility. The present study used isometric and work loop testing protocols to uniquely investigate the effects of 8 weeks of voluntary wheel running on the contractile performance of isolated dynapenic soleus and diaphragm muscles of 38-week-old CD1 mice. When compared with untrained controls, voluntary wheel running induced significant improvements in maximal isometric stress and work loop power, a reduced resistance to fatigue, but greater cumulative work during fatiguing work loop contractions in isolated muscle. These differences occurred without appreciable changes in lactate dehydrogenase, citrate synthase, sarco-endoplasmic reticulum ATPase or myosin heavy chain expression synonymous with this form of training in younger rodent models. Despite the given improvement in contractile performance, the average running distance significantly declined over the course of the training period, indicating that this form of training may not be sufficient to fully counteract the longer-term ageing-induced decline in skeletal muscle contractile performance. Although these results indicate that regular low-intensity physical activity may be beneficial in offsetting the age-related decline in skeletal muscle contractility, future work focusing on the maintenance of a healthy body mass with increasing age and its effects on myosin-actin cross-bridge kinetics and Ca2+ handling is needed to clarify the mechanisms causing the improved contractile performance in trained dynapenic skeletal muscle.