Increased Adiposity is Associated with Altered Skeletal Muscle Energetics.

The objective of this pilot study was to characterize relationships between skeletal muscle energy metabolism and body composition in healthy adults with varied amounts and distribution of adipose tissue. In vivo muscle energetics were quantified using dynamic 31 P magnetic resonance spectroscopy with knee extension exercise standardized to subject lean body mass. Spearman correlation analysis examined relationships between muscle metabolism indices and measures of adiposity including body mass index (BMI), total body fat, and quadriceps intermuscular adipose tissue (IMAT). Post-hoc partial correlations were examined controlling for additional body composition measures. Kruskal-Wallis tests with Dunn-Sidak post-hoc comparisons evaluated group differences in energy metabolism based on body composition profiles (i.e. lean, normal-weight obese, and overweight-obese) and IMAT tertiles. BMI negatively correlated with end-exercise muscle pH after correcting for IMAT and total body fat (r=-0.46, p=.034). Total adiposity negatively correlated with maximum oxidative capacity after correcting for IMAT (r=-0.54, p=.013). IMAT positively correlated with muscle proton buffering capacity after correcting for total body fat (r=0.53, p=.023). Body composition groups showed differences in end-exercise fall in [PCr] with normalized workload (p=.036; post-hoc: overweight-obese < lean, p=.029) and maximum oxidative capacity (p=.021; post-hoc: normal-weight obese < lean, p=.016). IMAT tertiles showed differences in end-exercise fall in [PCr] with normalized workload (p=.035; post-hoc: 3rd < 1st , p=.047). Taken together, these results support increased adiposity is associated with reduced muscle energetic efficiency with more reliance on glycolysis, and when accompanied with reduced lean mass, is associated with reduced maximum oxidative capacity.