LunHab: interactive effects of a 10 day sustained exposure to hypoxia and bedrest on aerobic exercise capacity in male lowlanders

Abstract

What is the central question of this study? What are the distinct and interactive effects of a 10 day exposure to hypoxia and horizontal bedrest on the whole-body peak oxygen uptake and on the regional cerebral and skeletal muscle tissue oxygenation during upright cycle ergometry in male lowlanders? What is the main finding and its importance? A 10 day sustained exposure to hypoxia aggravates the bedrest-induced reduction in peak oxygen uptake during dynamic exercise engaging large muscle groups, but mitigates the skeletal muscle oxidative capacity impairment elicited by bedrest. The study examined the interactive effects of a 10 day exposure to hypoxia and bedrest on the whole-body peak oxygen uptake (V̇O2 peak ) during maximal exercise and on skeletal muscle and cerebral oxygenation during submaximal exercise. Nine males underwent three 10 day confinements, in a Latin-square order, as follows: (i) a normoxic bedrest [NBR; partial pressure of inspired O (PI,O2) = 134.2 ± 0.7 mmHg]; (ii) a hypoxic bedrest (HBR; PI,O2 = 102.9 ± 0.1 mmHg at day 1, 91.5 ± 1.2 mmHg at days 3-10); and (iii) a hypoxic ambulation (HAMB; PI,O2 as in HBR). Before, 1 (R+1) and 3 days (R+3) after each confinement, subjects performed exhaustive, incremental-load and moderate-intensity constant-load (CLTs) cycle-ergometry trials, while breathing either room air or a hypoxic gas mixture. During the CLTs, changes in the regional oxygenation of the cerebral frontal cortex and the vastus lateralis and intercostal muscles were monitored with near-infrared spectroscopy. At R+1, the confinement-related impairment in V̇O2 peak was greater after HBR than after NBR or HAMB, regardless of whether the trial was performed in room air or hypoxia (HBR, -16.2%; NBR, -8.3%; HAMB, -4.1%; P = 0.001). During the CLTs, bedrest aggravated the exercise-induced reduction in locomotor and respiratory muscle oxygenation (P ≤ 0.05); an effect that was less after HBR than after NBR (P ≤ 0.05). The hypoxic exercise-induced cerebral vasodilatory response was blunted by HBR, probably because of the marked hyperventilation-dependent hypocapnia, attendant to the sustained hypoxic stimulus. Hence, short-term exposure to hypoxia potentiates the reduction in V̇O2 peak , but it mitigates the impairment in skeletal muscle oxidative capacity induced by bedrest.

Exercise temperature regulation following a 35‐day horizontal bedrest

“…This finding is in line with the results from other investigations, wherein the post-bedrest exercise provocation was conducted at a fixed absolute intensity (Greenleaf & Reese, 1980;Lee et al, 2002). The response appeared to be independent of any bedrest-related variation in the rate of heat production, judging by the similarV O 2 and H prod values attained in the PRE and POST-A trials, an observation that indeed is consistent with that reported in other bedrest studies (Convertino, 1996;Greenleaf & Reese, 1980;Keramidas et al, 2017;Lee et al, 2002). Still the 35 days of bedrest diminished the restingT sk by ∼1.5 • C and blunted the exercise-induced increase inT sk .…”

Exercise cardiorespiratory and thermoregulatory responses in normoxic, hypoxic, and hot environment following 10-day continuous hypoxic exposure

“…Thus, we opted for running the performance tests as soon as possible following the cessation of the hypoxic acclimatization. The timing of the exercise trials following hypoxic acclimatization could have also benefited V O 2max in NOR and HE (33). This hypothesis is supported by the fact that all the NOR and most of the HE trials were conducted on the second and third day post acclimatization when plasma volume is recovering (21).…”

‘White Mars’ – nearly two decades of biomedical research at the Antarctic Concordia station

“…Other ground‐based platforms have also specifically looked at physiological and psychological alterations induced by a changing environment, e.g. by conducting bedrest studies in hypoxic environments (PlanHab and Lunhab studies; Ciuha, Eiken, & Mekjavic, 2015; Keramidas, Mekjavic, & Eiken, 2017; McDonnell, Eiken, Frings‐Meuthen, Rittweger, & Mekjavic, 2019; Rullman, Mekjavic, Fischer, & Eiken, 2016; Salvadego et al., 2018; Šket et al., 2017; Strewe et al., 2017, 2018a). The ESA aims to further build upon this in the future and has initiated preparations for a 60‐day head down tilt bedrest study at the Planica Nordic Centre in Slovenia, allowing environmental pressure and oxygen parameters to be altered.…”