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: This study aimed 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 completemagnetic resonance imaging (MRI) measured adipose tissue and SMM pre- and postintervention. Macronutrient intake was assessed for a subsample of participants. Supervised exercise was performed by walking on a treadmill for durations ranging from 12 to 24 wk at intensities between 50% and 75% of VO2peak. Results: All MRI-measured adipose tissue depots were reduced, and cardiorespiratory fitness was increased by aerobic exercise compared with 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 (-0.310 +/- 0.150 kg, P = 0.039) and upper body SMM (-0.273 +/- 0.121 kg, P = 0.025) compared with control. No between-group difference was observed for change in leg SMM ( P > 0.10). A negative association was observed between the relative change in body weight and change in total (R-2 = 0.37, P < 0.001), upper body (R-2 = 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 > 0.10). Conclusions: Aerobic exercise performed while walking preserves, but does not increase, SMM in exercising muscle of adults. SMM not directly targeted by aerobic exercise may not be maintained.