Adjustments of pulmonary O_2 uptake and muscle deoxygenation during ramp incremental exercise and constant-load moderate-intensity exercise in young and older adults

摘要

The matching of muscle O_2 delivery to O_2 utilization can be inferred from the adjustments in muscle deoxygenation (A[HHb]) and pulmonary O_2 uptake (Vo2P). This study examined the adjustments of Vo_(2P )and delta[HHb] during ramp incremental (RI) and constant-load (CL) exercise in adult males. Ten young adults (YA; age: 25 +- 5 yr) and nine older adults (OA; age: 70 +- 3 yr) completed two RI tests and six CL step transitions to a work rate (WR) corresponding to 1) 80% of the estimated lactate threshold (same relative WR) and 2) 50 W (same absolute WR). Vo_(2p) was measured breath by breath, and A[HHb] of the vastus lateralis was measured using near-infrared spectroscopy. A[HHb]-WR profiles were normalized from baseline (0%) to peak A[HHb] (100%) and fit using a sigmoid function. The sigmoid slope (d) was greater (P < 0.05) in OA (0.027 +- 0.01 %/W) compared with YA (0.017 +- 0.01%/W), and the cld value (a value corresponding to 50% of the amplitude) was smaller (P < 0.05) for OA (133 +- 40 W) than for YA (195 +- 51 W). No age-related differences in the sigmoid parameters were reported when WR was expressed as a percentage of peak WR. Vo_(2p) kinetics compared with A[HHb] kinetics for the 50-W transition were similar between YA and OA; however, A[HHb] kinetics during the transition to 80% of the lactate threshold were faster than VO_(2P) kinetics in both groups. The greater reliance on O_2 extraction displayed in OA during RI exercise suggests a lower O_2 delivery-to-O_2 utilization relationship at a given absolute WR compared with YA.