Interrelation of 31P-MRS metabolism measurements in resting and exercised quadriceps muscle of overweight-to-obese sedentary individuals

Phosphorus magnetic resonance spectroscopy (31P‐MRS) enables the non‐invasive evaluation of muscle metabolism. Resting Pi‐to‐ATP flux can be assessed through magnetization transfer (MT) techniques, and maximal oxidative flux (Qmax) can be calculated by monitoring of phosphocreatine (PCr) recovery after exercise. In this study, the muscle metabolism parameters of 13 overweight‐to‐obese sedentary individuals were measured with both MT and dynamic PCr recovery measurements, and the interrelation between these measurements was investigated. In the dynamic experiments, knee extensions were performed at a workload of 30% of maximal voluntary capacity, and the consecutive PCr recovery was measured in a quadriceps muscle with a time resolution of 2 s with non‐localized 31P‐MRS at 3 T. Resting skeletal muscle metabolism was assessed through MT measurements of the same muscle group at 7 T. Significant linear correlations between the Qmax and the MT parameters kATP (r = 0.77, P = 0.002) and FATP (r = 0.62, P = 0.023) were found in the study population. This would imply that the MT technique can possibly be used as an alternative method to assess muscle metabolism when necessary (e.g. in individuals after stroke or in uncooperative patients). Copyright © 2013 John Wiley & Sons, Ltd. We showed that mitochondrial capacity, determined by the maximal oxidative flux from PCr‐recovery kinetics, correlates with the Pi‐to‐ATP flux at rest, as well as with the creatine‐kinase flux at rest in overweight‐to‐obese sedentary subjects. This would suggest that magnetization transfer (MT) could provide a marker of skeletal muscle metabolism that correlates with exercise–recovery experiments. We also showed that the time constant of PCr recovery correlates with MT values only if there is low variability in end‐exercise pHi.