Does Aerobic Exercise Increase Skeletal Muscle Mass in Female and Male Adults?

INTRODUCTION:It is uncertain whether aerobic exercise in the form of walking contributes to the preservation or increase in total or regional skeletal muscle mass (SMM). PURPOSE:To determine the effects of aerobic exercise on total and regional (upper body verses leg SMM) in male (n = 105) and female (n = 133) adults with overweight and obesity. METHODS:A retrospective analysis of data from four randomized controlled trials. Participants included those who completed the given trial (Control, n = 63; Intervention, n = 175), and with complete magnetic resonance imaging (MRI) measured adipose tissue and SMM pre- and post-intervention. Macronutrient intake was assessed for a sub-sample of participants. Supervised exercise was performed by walking on a treadmill for durations ranging from 12 to 24 weeks at intensities between 50 to 75% of VO2peak. RESULTS:All MRI-measured adipose tissue depots were reduced, and cardiorespiratory fitness was increased by aerobic exercise compared to controls (P < 0.001). Independent of baseline SMM, aerobic exercise was associated with a small reduction (estimated mean difference ± standard error) in whole body SMM (-.310 ± .150 kg, P = 0.039) and upper body SMM (-.273 ± .121 kg, P = 0.025) compared to control. No between group difference was observed for change in leg SMM (P > .10). A negative association was observed between the relative change in body weight and change in total (R2 0.37, P < 0.001), upper body (R2 0.21, P < 0.001) and leg SMM (R2 0.09, P = 0.701). The SMM to adipose tissue ratio increased in response to aerobic exercise and was positively associated with weight loss (P < 0.001). Change in SMM was not associated with dietary protein intake (P > .10). CONCLUSIONS:Aerobic exercise performed while walking preserves, but does not increase, SMM in exercising muscle of adults. Skeletal muscle mass not directly targeted by aerobic exercise may not be maintained.