Skeletal Muscle Mitochondrial Bioenergetics in Pregnancy: A Comparison of In Vivo and In Vitro Outcomes

Abstract Purpose Exercise-mediated adaptations to mitochondria are well established in non-gravid populations; however, the extent to which these adaptations occur during pregnancy remains unclear. Therefore, the objective of this study was to compare skeletal muscle mitochondrial bioenergetics in physically Active (A, n=10) versus Sedentary (S, n=9) pregnant women. Methods Groups were matched for age, race, and pre-gravid BMI and were studied in the second (T2; weeks 21-25) and third trimester (T3; weeks 31-35). Free-living physical activity was assessed by accelerometry and aerobic fitness by VO2peak testing. In vivo mitochondrial capacity was assessed by 31P-magnetic resonance spectroscopy. Primary skeletal muscle myotubes were obtained via muscle biopsy between late T2 and early T3. Mitochondrial in vitro respiration was assessed by high-resolution respirometry, and mitochondrial content was measured by Western blot and enzyme activity. Results Despite a decline in physical activity across gestation, A maintained a higher VO2peak at T2 (p0.05) and T3 (p0.01) compared to S. There were no differences in PCr recovery time between groups or timepoints. Myotube mitochondrial respiratory capacity was similar between groups; however, compared to S, A demonstrated increased expression of mitochondrial complexes I, II, and IV (all p0.05) proteins. Additionally, myotube mitochondrial efficiency (ATP/O ratio) measures positively correlated with maternal VO2peak at T3 (r=0.49, p0.05), suggesting a link between fitness and mitochondrial efficiency. Conclusions These findings suggest that late pregnancy may blunt mitochondrial adaptations to aerobic exercise despite a preservation of cardiovascular fitness. Future studies are needed to determine whether increasing activity throughout gestation can enhance mitochondrial respiration.