Effect of weight reduction, obesity predisposition, and aerobic fitness on skeletal muscle mitochondrial function

We used P-31 magnetic resonance spectroscopy to measure maximal mitochondrial function in 12 obesity prone women before and after diet-induced weight reduction and in 12 matched, never-obese, and 7 endurance-trained controls, Mitochondrial function was modeled after maximum-effort plantar flexion from the phosphocreatine recovery time constant (TCPCr), the ADP recovery time constant (TCADP), and the rate of change in PCr during the first 14 s of recovery (OxPhos). Weight reduction was not associated with a significant change in mitochondrial function by TCPCr, TCADP, Or OxPhos. Mitochondrial function was not different between postobese and never-obese controls by TCPCr [35.1 +/- 2.5 (SE) vs. 34.6 +/- 2.5 s], TCADP (22.9 +/- 1.8 vs. 21.2 +/- 1.8 s), or OxPhos (0.26 +/- 0.03 vs. 0.25 +/- 0.03 mM ATP/s), postobese vs. never-obese, respectively. However, TCADP was significantly faster (14.5 +/- 2.3 s), and OxPhos was significantly higher (0.38 +/- 0.04 mM ATP/s) in the endurance-trained group. These results suggest that maximal mitochondrial function is not impaired in normal-weight obesity-prone women relative to their never-obese counterparts but is increased in endurance-trained women.