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 nongravid 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 (n = 10) vs sedentary (n = 9) pregnant women. Methods Groups were matched for age, race, and pregravid body mass index 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 peak oxygen uptake (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, active women maintained a higher VO2peak at T2 (P < .05) and T3 (P < .01) compared with sedentary. There were no differences in phosphocreatine recovery time between groups or timepoints. Myotube mitochondrial respiratory capacity was similar between groups; however, compared with sedentary mothers, active mothers demonstrated increased expression of mitochondrial complexes I, II, and IV proteins (all P < .05). Additionally, myotube mitochondrial efficiency (adenosine triphosphate-to-oxygen consumption ratio) measures were positively correlated with maternal VO2peak at T3 (r = 0.49, P < .05), suggesting a link between fitness and mitochondrial efficiency. Conclusion 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.