Braden M. R. Gravelle

Adjustments of pulmonary O2 uptake and muscle deoxygenation during ramp incremental exercise and constant-load moderate-intensity exercise in young and older adults

The matching of muscle O(2) delivery to O(2) utilization can be inferred from the adjustments in muscle deoxygenation (Δ[HHb]) and pulmonary O(2) uptake (Vo(2p)). This study examined the adjustments of Vo(2p) and Δ[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 Δ[HHb] of the vastus lateralis was measured using near-infrared spectroscopy. Δ[HHb]-WR profiles were normalized from baseline (0%) to peak Δ[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 c/d 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 Δ[HHb] kinetics for the 50-W transition were similar between YA and OA; however, Δ[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.

Duration of “Phase I” V̇o2p: a comparison of methods used in its estimation and the effects of varying moderate-intensity work rate

The present study was designed to investigate whether absolute work rate (WR) affects Phase I pulmonary oxygen uptake (Vo(2)(p)) duration during moderate-intensity (Mod) exercise and to compare two methods for estimating Phase I Vo(2)(p) duration (P(I-Dur)). Fourteen males (24 ± 5 yr) each completed 4-8 repetitions of Mod transitions from 20 W to 50, 70, 90, 110, and 130 W. P(I-Dur) was identified by 1) a marked decrease in both respiratory exchange ratio and end-tidal partial pressure of O(2) following exercise onset [i.e., visual inspection of three independent reviewers, and the average (Avg) of the two most similar values]; or 2) the intersection (time delay, TD) of the first and second components in a biexponential nonlinear regression of the entire Vo(2)(p) response from exercise onset. P(I-Dur) did not differ among WRs (P > 0.05), regardless of the estimation method used. No differences were detected between Avg and TD (time in s) at any of the five WRs (50 W, 21 ± 6 vs. 23 ± 10 s; 70 W, 23 ± 9 vs. 23 ± 7 s; 90 W, 24 ± 3 vs. 22 ± 5 s; 110 W, 23 ± 6 vs. 22 ± 6 s; 130 W, 21 ± 6 vs. 21 ± 7 s; P > 0.05 for Avg and TD, respectively). Broad limits of agreement within Bland-Altman plots revealed relatively weak agreement among reviewers for individual estimation of P(I-Dur). A nonsignificant correlation coefficient (r = 0.13) and broad limits of agreement suggest disparity between individual Avg and TD estimates of P(I-Dur). The present data do not support a role for Mod WR in determining P(I-Dur) per se. Furthermore, this study illustrated a poor agreement of P(I-Dur) estimates derived from two different, but accepted methods.