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

Abstract

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.

Slower V˙O2 Kinetics in Older Individuals

“…This suggests that the slower dynamic adjustment of oxidative phosphorylation typically observed in older individuals might be secondary to other factors such as training status, instead of being exclusively determined by aging per se. Indeed, in three other studies in which V O 2 kinetics responses were compared in older and young individuals, the rate of adjustment of oxidative phosphorylation was similar between groups (12,13,38). In addition, a recent paper has demonstrated that older, chronically trained men have V O 2 kinetics that is similar to those of young individuals (39).…”

“…Babcock and colleagues originally noted little change in the HR dynamics across age (30-80 yr) (3) and that with training the faster HR kinetics were not related to the faster V O 2 kinetics (2). Nevertheless, other studies have found that THR was significantly greater in older compared with young individuals (14,22,38) with a significant correlation (r = 0.76) between THR and TV O 2 in one of those studies (22). However, there are also data to support the idea that even if a slower adjustment of HR occurs in older participants, compensatory mechanisms might take place to distribute a larger percentage of the cardiac output to the active muscles so that muscle blood flow is not compromised (71).…”

“…It is now generally accepted that V O 2 kinetics becomes progressively slower with aging. Studies evaluating the V O 2 kinetics responses in older individuals (generally, age 65 yr and older) have shown TV O 2 values ranging from È30 s to È60 s for the group average response (2,3,8,(12)(13)(14)(15)22,23,38,40,41,57,58,61,76,80), whereas the average group mean TV O 2 in young subjects normally ranges between 20 s and 45 s (11)(12)(13)(14)(15)(22)(23)(24)36,38,40,48,57,58,61,76). From these group mean values reported in older and young populations, it seems evident that, although older participants display an overall slower adjustment of V O 2 during exercise transitions from baseline to a higher intensity within the moderate-intensity domain, there is also an ''overlapping'' area where older and young individuals have a similar V O 2 kinetics response.…”

Assembling more O2 uptake responses: Is it possible to merely stack the repeated transitions?

“…Other authors further averaged the responses into 5 s (e.g. Gravelle et al, 2012) or into 10 s (e.g. Salvadego et al, 2010) time intervals, although none of them provide a justification for these procedures; an alternative method requiring the averaging of more data according to the number of repetitions was used by Murgatroyd et al (2011).…”

Estudo das equações de referência dos parâmetros de função pulmonar em repouso e ao exercício em amostra de idosos hígidos da população brasileira

“…Essas alterações refletem, em grande parte, o declínio da capacidade oxidativa mitocondrial, gerando maior dependência de metabolismo anaeróbico em pessoas idosas (36) (38) . Alterações na capacidade de integração sensorial também são descritas com o envelhecimento.…”