A decline in skeletal muscle function is thought to be a key factor contributing to the decreased functional capacity and quality of life associated with aging. Although the exact mechanism is not fully understood, impaired mitochondrial and microvascular function are thought to play a major role. A complicating factor in determining the physiological mechanisms of aging is the fact that aging typically coincides with a decline in physical fitness due to lifestyle changes. PURPOSE: To evaluate age-related differences in skeletal muscle oxidative function using near-infrared spectroscopy (NIRS), and to examine the role of physical fitness. METHODS: Nineteen young (Y: 26.2 ± 3.0 yrs) and twenty elderly (E: 62.4 ± 4.3 yrs) adults participated in this study. Skeletal muscle oxidative function was evaluated during whole-body exercise (cycling) and isolated muscle work (handgrip exercise) using NIRS. Muscle oxyhemoglobin saturation (SmO2) was measured in the leg and forearm. Vascular occlusions were applied at rest and immediately following submaximal cycling (CY) and handgrip (HG) exercise bouts at various intensities. End-exercise SmO2 values were calculated as the average SmO2 values during the last 30 s of each work bout, and muscle oxygen consumption (mVO2) was derived from the initial linear decrease in SmO2 during vascular occlusions. RESULTS: No differences were found in resting mVO2 for leg or forearm (all P > 0.05). Submaximal CY work rates were similar at low intensity (E: 81 ± 28 W vs Y: 89 ± 25 W, P = 0.17), but significantly lower for the elderly during high intensity (E: 182 ± 59 W vs Y: 217 ± 49 W, P = 0.02). All four submaximal HG work rates were similar for Y and E (P > 0.05). Although SmO2 responses during both exercise modes were more pronounced in Y, no significant differences between Y and E were found in end-exercise SmO2 values or mVO2 (all P > 0.05). CONCLUSION: When exercising at roughly equal absolute and relative work rates, muscle function was similar in E and Y, both during whole body CY as well as during isolated HG exercise. Since absolute and relative work rates were reasonably similar for both groups, the results indicate that not aging, but physical fitness level might be the determinant for the decreased muscle function that is thought to accompany aging.
Read full abstract