PURPOSE To investigate the influence of age on the relationship between pulmonary O2 uptake and local muscle deoxygenation. METHODS Five young (Y),(mean age 26±3y), and six older males (O),(mean age68±3y), performed ramp cycling exercise (25W/min) to the limit of tolerance. Pulmonary O2 uptake was measured breath-by-breath. Oxy-(O2Hb), deoxy-(HHb), total (Hbtot) hemoglobin/myoglobin and tissue oxygenation index (TOI) of the vastus lateralis were measured continuously by near-infrared spectroscopy (NIRS; Hamamatsu, NIRO 300). NIRS-HHb data were expressed as a percentage of the maximum increase in HHb during the exercise period (HHb,%max). HHb(%max) and TOI were compared between Y and O at similar submaximal VO2's (1.0, 1.25, 1.50, 1.75, 2.0 L/min). RESULTS VO2max was 2.28 (±0.27) L/min in O and 3.81 (±0.43) L/min in Y. The maximal increase in HHb was similar in O (22 ± 7 μ M) and Y (28 ± 12 μ M). At a given submaximal VO2 the O used a significantly greater proportion of their HHb reserve compared to the Y. For example, at VO2 1.75 l/min, HHB(%max) was 64 ± 19% in O versus 27 ± 6% in Y. The TOI was also significantly lower throughout submaximal exercise in O versus Y. CONCLUSIONS The O showed a similar increase in HHb at maximum exercise as in the Y. Throughout exercise, at a given VO2, the greater HHb and the lower TOI in O compared with Y provides evidence of a lower muscle blood flow throughout exercise in the elderly. Supported by NSERC, Canada
Six male subjects [23 yr (SD 4)] performed repetitions (6–8) of two-legged, moderate-intensity, knee-extension exercise during two separate protocols that included step transitions from 3 W to 90% estimated lactate threshold (θ L ) performed as a single step (S3) and in two equal steps (S1, 3 W to ∼45% θ L ; S2, ∼45% θ L to ∼90% θ L ). The time constants (τ) of pulmonary oxygen uptake (V̇o 2 ), leg blood flow (LBF), heart rate (HR), and muscle deoxygenation (HHb) were greater ( P < 0.05) in S2 (τV̇o 2 , ∼52 s; τLBF, ∼ 39 s; τHR, ∼42 s; τHHb, ∼33 s) compared with S1 (τV̇o 2 , ∼24 s; τLBF, ∼21 s; τHR, ∼21 s; τHHb, ∼16 s), while the delay before an increase in HHb was reduced ( P < 0.05) in S2 (∼14 s) compared with S1 (∼20 s). The V̇o 2 and HHb amplitudes were greater ( P < 0.05) in S2 compared with S1, whereas the LBF amplitude was similar in S2 and S1. Thus the slowed V̇o 2 response in S2 compared with S1 is consistent with a mechanism whereby V̇o 2 kinetics is limited, in part, by a slowed adaptation of blood flow and/or O 2 transport when exercise was initiated from a baseline of moderate-intensity exercise.
