Initiating exercise training in late middle age minimally protects muscle contractile function and increases myocyte oxidative damage in senescent rats

Age-related loss of muscle mass and function exhibits a marked acceleration from late middle age to senescence and exercise training is one method that has been proposed to slow this process. The purpose of this study was to determine if long-term treadmill exercise training initiated at late middle age could increase endogenous antioxidant enzyme activity and attenuate the loss of skeletal muscle contractile properties in the gastrocnemius/plantaris (GAS/Plan) and soleus (SOL) muscles of senescent rats (34–36 mo) through a decrease in oxidative damage. Male Fisher 344 × Brown Norway F1-hybrid rats underwent 5–7 mo of treadmill training beginning at late middle age (29 mo). A 7 mo sedentary adult group was used to investigate age-related changes. Aging caused an increase in antioxidant enzyme activities; however, only SOD activity was further increased with exercise training. Exercise training did not attenuate the decrease in twitch or tetanic tension of the GAS/Plan or SOL. It did, however, prevent the increase in twitch half relaxation time of the SOL muscle only. Oxidative damage, as reflected in carbonyl content, was increased with age and even further with exercise training in the GAS muscle. Muscle fibre cross sectional area was decreased with age and even further with exercise training. Interestingly, small muscle fibres showed the highest accumulation of carbonyls. Overall, despite an augmentation of select antioxidant enzyme activities, exercise training from late middle age through to senescence had minimal benefits for muscle contractile properties, perhaps in part due to exacerbated oxidation.

Research Highlights
► Initiating endurance exercise training at late middle age augments the age-associated increase in some endogenous antioxidants in senescent skeletal muscle.
► Initiating endurance exercise training at late middle age does not protect senescent skeletal muscle contractile function.
► Despite an increased endogenous antioxidant capacity, endurance training exacerbated the age-related increase in myocyte cytoplasmic carbonyl accumulation in senescent skeletal muscle, suggesting an inability to cope with the exercise-induced oxidative stress in senescence.
► Senescent skeletal muscle has a diminished capacity to positively adapt to endurance training.