The Effects of 120 Days Confinement During the SIRIUS Project on Physiological Kinetics and Inhibitory Control

Purpose: Sojourns in microgravity, like on the international space station (ISS) and especially during future long-term space travel, affect cardiorespiratory and cognitive parameters with influences on mission success, fitness, and overall well-being. Countermeasures are investigated with respect to their feasibility in space, time-efficiency, and overall beneficial effects on physical and cognitive performance. While both interval (INT) and continuous (CON) physical exercise training show positive effects on heart rate (HR) and oxygen uptake (V̇O2) capacities and kinetics in terrestrial settings, research for space application is still pending. Furthermore, in laboratory conditions, physical exercise positively interacts with cognitive performance, whereas confinement is known for the detrimental effects of inactivity and less external stimuli. Therefore, this interaction should be implemented in the analysis of countermeasures for confinement and microgravity-contexts. We expected (I) negative effects of confinement on cognitive performance and (II) physical fitness improvements, especially from INT. Methods: Six participants (34 ± 6 years, 3 females) spent 120 days in confinement, conducting eight weeks of CON, followed by eight weeks of INT aerobic treadmill exercise in a crossover design. Changes in cardiorespiratory fitness and cognitive performance were assessed with an exercise test protocol, including pseudo-random work rate changes (PRBS), constant workrate phases, and incremental exercise before the start of confinement (PRE), five times during confinement (mission day (MD) 9 (±1;), 29 (±1), 57 (±1), 87 (±1), and 117 (±1)), and after the termination of the mission phase (POST). HR was measured beat-to-beat, and V̇O2 assessed breath-by-breath. From interpolated 1 s data, kinetics information were derived using time series analysis on the PRBS part. Capacities of V̇O2 and HR were determined from the last 30 s of incremental exercise. Within the exercise test, the Eriksen Flanker task tested inhibitory control during REST, constant workrate at 3 (LOW), 6 (MID), and 9 km h-1 (HIGH), and during recovery (REC). Results: For peak values significant time effects for HR (P = 0.025), V̇O2 (P = 0.012), and respiratory exchange ratio (RER) (P = 0.001) with lower values during confinement were shown. Kinetics of HR and V̇O2 revealed a significant time effect (both < 0.05). CON and INT exercise both seemed to speed HR kinetics during the mission with slightly better effects for INT. Inhibitory control was neither altered during rest, constant work rate nor at recovery by 15 weeks of confinement. Conclusion: While the positive effects of INT and CON aerobic exercise, as known from laboratory studies, were also evident in HR kinetics during confinement, no improvement can be reported for V̇O2 kinetics. This might be due to the lack of general physical activity during confinement, which was merely compensated and not improved by the applied exercise countermeasure. In addition, this study proved the successful implementation of cognitive testing within our physical exercise test during confinement. Reaction times (RT) and accuracy (ACC) of the Eriksen Flanker task were not significantly altered. Yet, descriptively slower RTs were observed during confinement compared to PRE and POST and might be attributed to less external stimuli, a decline in participants’ mood, or general confinement effects.