The aim of this study was to compare muscle O2 dynamics during exercise among elderly (n = 10, age: 73 ± 3 years), middle-aged (n = 9, age: 50 ± 6 years), and young (n = 10, age: 25 ± 3 years) adults. The subjects performed ramp bicycle exercise until exhaustion. Muscle O2 saturation (SmO2) and relative changes from rest in oxygenated hemoglobin/myoglobin (∆oxy-Hb/Mb), deoxygenated hemoglobin/myoglobin (∆deoxy-Hb/Mb), and total hemoglobin concentration (∆total-Hb) were monitored continuously at the vastus lateralis muscle by near-infrared spatial resolved spectroscopy. At given absolute workloads, SmO2 and ∆oxy-Hb/Mb were significantly lower in elderly than the other groups, while ∆deoxy-Hb/Mb, ∆total-Hb, and pulmonary O2 uptake (VO2) were similar among the three groups. In contrast, there were no significant differences in muscle O2 dynamics during submaximal exercise between middle-aged and young subjects. Muscle O2 dynamics may be relatively preserved in early stages of aging, although muscle deoxygenation is enhanced in late stages of aging, probably due to reduced convective O2 supply. Moreover, change in SmO2 was significantly positively correlated with peak VO2 in the elderly, while a significant negative relationship was observed in middle-aged and young subjects. In late stages of aging, diminished peak VO2 may be caused by attenuated convective O2 transport, while reduced peak VO2 can be explained by lowered muscle O2 extraction in early stages of aging.
Keywords: Convective O2 transport; Elderly adults; Middle-aged adults; Muscle O2 extraction; Young adults.