Skeletal Muscle Deoxygenation and Its Relationship to Aerobic Capacity During Early and Late Stages of Aging

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.