Abstract

Muscle atrophy is a highly prevalent condition among older adults, and results from reduced muscle mass and fiber cross-sectional area. Resistive exercise training and moderate (30-40%) caloric restriction may reduce the rate of sarcopenia in animal models. We tested the hypothesis that lifelong, voluntary exercise combined with mild (8%) caloric restriction would attenuate the reduction of muscle fiber cross-sectional area in the rat plantaris. Fischer-344 rats were divided into: young adults (6 mo) fed ad libitum (YAL); 24 mo old fed ad libitum (OAL); 24 mo old on 8% caloric restriction (OCR); lifelong wheel running with 8% CR (OExCR). Plantaris fiber cross-sectional area was significantly lower in OAL than YAL (-27%), but protected in OCR and OExCR, while mass/body mass ratio was preserved in OExCR only. Furthermore, 8% CR and lifelong wheel running attenuated the age-induced increases in extramyocyte space and connective tissue. Citrate synthase activity decreased with age, but was not significantly protected in OCR and OExCR. Total hydroperoxides were higher in OAL than YAL, but were not elevated in OExCR, with out a change in MnSOD. IGF-1 levels were lower in OAL (-57%) than YAL, but partially protected in the OExCR group (+51%).