Oxidative metabolism in muscle.

Oxidative metabolism is the dominant source of energy for skeletal muscle. Near-infrared spectroscopy allows the non-invasive measurement of local oxygenation, blood flow and oxygen consumption. Although several muscle studies have been made using various near-infrared optical techniques, it is still difficult to interpret the local muscle metabolism properly. The main findings of near-infrared spectroscopy muscle studies in human physiology and clinical medicine are summarized. The advantages and problems of near-infrared spectroscopy measurements, in resting and exercising skeletal muscles studies, are discussed through some representative examples

Energy metabolism and interstitial fluid displacement in human gastrocnemius during short ischemic cycles

Energy metabolism and interstitial fluid displacement were studied in the human gastrocnemius during three subsequent 5-min ischemia-reperfusion periods [ischemic preconditioning (IP)]. The muscle energy balance was assessed by combining near-infrared spectroscopy (NIRS) and 31P-nuclear magnetic resonance spectroscopy (31P-NMRS). The interstitial fluid displacement was determined by combining NIRS and 23Na-NMRS. No changes in total energy consumption or in the fractional contribution of the underlying energy sources (aerobic glycolysis, anaerobic glycolysis, and Lohmann reaction) were observed in the muscle during the tested IP protocol. Oxygen consumption in the muscle region of interest, as estimated by NIRS, was approximately 8 micromol . 100 g-1 . min-1 and did not change during IP. Phosphocreatine and ATP concentrations did not change over the whole experimental period. A slight but significant (P < 0.05) increase in intracellular pH was observed. Compared with the control, a 10% greater interstitial fluid content per muscle unit volume was observed at the end of the IP protocol. It is concluded that, at variance with cardiac muscle, repeated 5-min ischemia-reperfusion cycles do not induce metabolic changes in human gastrocnemius but alter the interstitial fluid readjustment. The techniques developed in the present study may be useful in identifying protocols suitable for skeletal muscle preconditioning and to explain the functional basis of this procedure