Exercise Effects on Mitochondrial Function and Lipid Metabolism during Energy Balance.

INTRODUCTION/PURPOSE Aerobic exercise training (AET) has been shown to improve mitochondrial bioenergetics and upregulate proteins related to lipid metabolism. However, it remains to be determined if these alterations associated with AET persist when measured in energy balance (EB) in the days following the last bout of training. . The purpose of the study was to test the hypothesis that improvements in skeletal muscle mitochondrial function induced by AET observed in previous literature would persist when measured after restoring EB conditions 72 hours removed from the last exercise bout. METHODS Participants were 14 premenopausal women (age = 31.2 ± 6.7 years, BMI = 26.6 ± 5.1 kg/m). The AET program required 3 monitored training sessions per week for 8-16 weeks. Skeletal muscle biopsies were obtained at baseline and following 8-16 weeks of AET (≥72 hrs after the last exercise bout). All food was provided for 72 hours prior to biopsies and EB was managed 24 hours prior to testing within ±100 kcal of measured energy requirements using a whole-room calorimeter. Mitochondrial oxidative capacity was quantified in permeabilized muscle fibers from the vastus lateralis. RESULTS We found that AET increased coupled respiration (154%) and uncoupled respiration (90%) rates using a fatty acid substrate (palmitoyl carnitine) (P<0.05). However, when rates were normalized to complex IV activity (a marker of mitochondrial content), no significant differences were observed. Additionally, there were no changes in proteins known to mediate mitochondrial biogenesis or lipid transport and metabolism following AET. CONCLUSION 8-16 weeks of AET improved mitochondrial capacity under fatty acid substrate when assessed in EB, which appears to be due to mitochondrial biogenesis.