Living In Confinement Conditions: Physical Training Can Improve Muscular Oxygen Uptake and Heart Rate Kinetics

Abstract

PURPOSE: Inside the NASA Human Exploration Research Analog (HERA) facility the effects of 45 d of confinement in combination with restrictions for sleep and a defined physical training on muscular oxygen uptake (V’O2musc) kinetics and cardiovascular regulation during exercise was investigated. METHODS: To date, fourteen healthy individuals (5 females, 9 males, 37±7 y, 23±3 kg∙m-2) were analyzed 8 d before (MD-8), during and 4 d after (MD+4) a simulated Space mission. A cycle exercise test with pseudo-random binary work rate changes (WR) of 30 W and 80 W and an incrementally increasing step protocol (25 W min-1) to assess peak oxygen uptake (V’O2peak) was applied. Heart rate (HR) and mean arterial blood pressure (MAP) were measured beat-to-beat and pulmonary oxygen uptake (V’O2pulm) breath-by-breath. V’O2musc was estimated from HR and V’O2pulm. Kinetics responses were assessed by maxima of the cross correlation function (CCFmax) between WR and the respective parameter indicate faster kinetics (Hoffmann et al., Eur J Appl Physiol 113:1745-1754, 2013). During the mission, exercise training sessions were scheduled every second day with a maximal HR restricted to below 85% of the age-related maximum. Sleep was restricted to 5 h per weekday and 8 h at the weekends. Differences in V’O2peak and kinetics from MD-8 to MD+4 were calculated and correlated with the values measured at MD-8 using the Pearson test. Level of significance was set to α = 5%. RESULTS: V'O2peak differed not significantly (P=0.221) between MD-8 (37.8±5.8 ml min-1 kg-1) and MD+4 (38.9±4.6 ml min-1 kg-1). Changes in CCFmax(HR) correlated significantly with CCFmax(HR) at MD-8 (r = -0.839, P < 0.001), changes in CCFmax(V’O2musc) correlated significantly with CCFmax(V’O2musc) at MD-8 (r = -0.641; P = 0.014) and the difference in V’O2peak correlated with V’O2peak at MD-8 (r = -0.614; P = 0.019). CONCLUSIONS: Exercise training during forty-five days of confinement in combination with sleep restrictions, may prevent from losses in cardio-muscular kinetics. Those individuals who started with slow kinetics or a low V’O2peak benefited from the exercise training during the mission. The volume and/or intensity of the exercise training intervention might have been higher during the HERA C4 missions compared to most of the crew members’ everyday life activities.