Effects of age on muscle energy metabolism and oxygenation in the forearm muscles

Purpose: The effects of aging on muscle metabolism and oxygenation have not yet been elucidated. We evaluated the effects of aging on energy metabolism and oxygenation in sedentary healthy subjects by simultaneously measuring P-31-magnetic resonance spectroscopy (MRS) and near-infrared spectroscopy (NIRS). Methods: Nine young (28.1 +/- 5.0 yr) and nine older (61.4 +/- 4.6 yr) healthy subjects were studied. The P-31-MR spectrum was obtained every 15 s during and after hand gripping exercise. Intracellular pH (pHi) and PCr(PCr+Pi) [PCr: phosphocreatine, Pi: inorganic phosphate] were calculated as an index of energy metabolism. The time constant of the PCr/(PCr+Pi) recovery (tau PCr) was calculated. With NIRS, we evaluated the recovery rates of oxygenated (RHbO(2)) and deoxygenated hemoglobin (RHb) during the initial 10 s of recovery. Results: The PCr/(PCr+Pi) and pHi at rest and at completion of the exercise and tau PCr did not differ between young and older subjects. However, RHbO(2) and RHb were significantly slower in older subjects than in young subjects. Conclusions: The results suggest that muscle,energy metabolism in the forearm muscle was not affected by aging. The slower RHbO(2) and RHb in older subjects suggested impaired O-2 supply, which was probably due to impaired peripheral circulation caused by the process of aging.