Key result
Hypoxic bed rest exaggerated the bed-rest-induced reduction in peak oxygen uptake compared to normoxic bed rest (-13.5% vs -8.6%; P=0.01).
Why the study?
Does hypoxic bed rest exaggerate the reduction in peak oxygen uptake compared to normoxic bed rest in male lowlanders?
RCT (n=10)
counterbalanced order
Does hypoxic bed rest exaggerate the reduction in peak oxygen uptake compared to normoxic bed rest in male lowlanders?
Absolute Event Rate: -13.5% vs -8.6%
p-value: p=0.01
Hypoxia exacerbates the bed-rest-induced decline in peak oxygen uptake, likely due to reduced convective O2 transport.
Small n=10 limits generalizability; leaves open additive effects of hypoxia plus bed rest on exercise capacity.
The study examined the effects of hypoxia and horizontal bed rest, separately and in combination, on peak oxygen uptake (V̇o2 peak) during upright cycle ergometry. Ten male lowlanders underwent three 21-day confinement periods in a counterbalanced order: 1) normoxic bed rest [NBR; partial pressure of inspired O2 (PiO2 ) = 133.1 ± 0.3 mmHg]; 2) hypoxic bed rest (HBR; PiO2 = 90.0 ± 0.4 mmHg), and 3) hypoxic ambulation (HAMB; PiO2 = 90.0 ± 0.4 mmHg). Before and after each confinement, subjects performed two incremental-load trials to exhaustion, while inspiring either room air (AIR), or a hypoxic gas (HYPO; PiO2 = 90.0 ± 0.4 mmHg). Changes in regional oxygenation of the vastus lateralis muscle and the frontal cerebral cortex were monitored with near-infrared spectroscopy. Cardiac output (CO) was recorded using a bioimpedance method. The AIR V̇o2 peak was decreased by both HBR (∼13.5%; P ≤ 0.001) and NBR (∼8.6%; P ≤ 0.001), with greater drop after HBR (P = 0.01). The HYPO V̇o2 peak was also reduced by HBR (-9.7%; P ≤ 0.001) and NBR (-6.1%; P ≤ 0.001). Peak CO was lower after both bed-rest interventions, and especially after HBR (HBR: ∼13%, NBR: ∼7%; P ≤ 0.05). Exercise-induced alterations in muscle and cerebral oxygenation were blunted in a similar manner after both bed-rest confinements. No changes were observed in HAMB. Hence, the bed-rest-induced decrease in V̇o2 peak was exaggerated by hypoxia, most likely due to a reduction in convective O2 transport, as indicated by the lower peak values of CO.
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Keramidas et al. (2016) conducted an RCT in Healthy (lowlanders) (n=10). Hypoxic bed rest (HBR) vs. Normoxic bed rest (NBR) was evaluated on peak oxygen uptake (V̇o2 peak) while inspiring room air (p=0.01). Hypoxic bed rest exaggerated the bed-rest-induced reduction in peak oxygen uptake compared to normoxic bed rest (-13.5% vs -8.6%; P=0.01).
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