Moderate Exercise Based on Artificial Gravity Preserves Orthostatic Tolerance and Exercise Capacity During Short-Term Head-Down Bed Rest

Abstract

Numerous countermeasures have been proposed to minimize microgravity-induced physical deconditioning, but their benefits are limited. The present study aimed to investigate whether personalized aerobic exercise based on artificial gravity (AG) mitigates multisystem physical deconditioning. Fourteen men were assigned to the control group (n=6) and the countermeasure group (CM, n=8). Subjects in the CM group were exposed to AG (2 Gz at foot level) for 30 min twice daily, during which time cycling exercise of 80-95 % anaerobic threshold (AT) intensity was undertaken. Orthostatic tolerance (OT), exercise tests, and blood assays were determined before and after 4 days head-down bed rest (HDBR). Cardiac systolic function was measured every day. After HDBR, OT decreased to 50.9 % and 77.5 % of pre-HDBR values in control and CM groups, respectively. Exercise endurance, maximal oxygen consumption, and AT decreased to 96.5 %, 91.5 % and 91.8 % of pre-HDBR values, respectively, in the control group. Nevertheless, there were slight changes in the CM group. HDBR increased heart rate, sympathetic activity, and the pre-ejection period, but decreased plasma volume, parasympathetic activity and left-ventricular ejection time in the control group, whereas these effects were eliminated in the CM group. Aldosterone had no change in the control group but increased significantly in the CM group. Our study shows that 80-95 % AT aerobic exercise based on 2 Gz of AG preserves OT and exercise endurance, and affects body fluid regulation during short-term HDBR. The underlying mechanisms might involve maintained cardiac systolic function, preserved plasma volume, and improved sympathetic responses to orthostatic stress.

Effectiveness of Resistive Vibration Exercise and Whey Protein Supplementation Plus Alkaline Salt on the Skeletal Muscle Proteome Following 21 Days of Bed Rest in Healthy Males

“…The novelty of the present study was to give subjects the correct recommended daily protein allowance throughout the baseline and bed rest. Whole-body functional outcomes such as reduced aerobic capacity and leg strength (Figure ) were consistent with previous reports − and demonstrate the negative effects of inactivity on these physiological variables. These changes represent early and clinically relevant physiological alterations that occur with imposed inactivity, confinement to beds, or space flight that may have negative biological consequences in terms of muscle insulin sensitivity.…”

Implementation of exercise countermeasures during spaceflight and microgravity analogue studies: Developing countermeasure protocols for bedrest in older adults (BROA)

“…The use of centrifugation ( Katayama et al, 2004 ) or LBNP ( Watenpaugh et al, 2000 ; Lee et al, 2007 ) with simultaneous high-intensity interval exercise has been very effective at maintaining aerobic fitness post-bedrest. Moderate-intensity cycling during artificial gravity also maintained O 2 max during four-day HDBR ( Li et al, 2017 ). The addition of resistance training to aerobic training with LBNP also maintained aerobic fitness post-HDBR ( Schneider et al, 2009 ).…”

“…Similarly, resistive vibration exercise prevented changes in LVEDV, LV mass and contractility following 21-day HDBR ( Greaves et al, 2019 ). Supine cycling alone (3 sessions x 30 min/day at 75% maximum HR) attenuated reductions to LVEDV and SV whilst maintaining cardiac mass and diastolic suction over 18 days of HDBR ( Dorfman et al, 2008 ; Shibata et al, 2010 ), whilst supine cycling at only 40 W and combined with artificial gravity at alternating 1–2 Gz (foot level) preserved resting supine HR and systolic function during 4-day HDBR ( Yang et al, 2011 ; Li et al, 2017 ). Overall, most HDBR studies provide evidence that aerobic and/or resistance exercise are beneficial for maintaining cardiac morphology and function, but differences in cardiac responses between concurrent and aerobic only countermeasures suggest the type and intensity of exercise is important for maintenance of cardiac function.…”

“…The intensities and modes of aerobic and resistance countermeasures during HDBR in combination with the subjects’ activity levels prior to bedrest contribute to observations of variable cardiac responses ( Dorfman et al, 2007 ; Shibata et al, 2010 ; Yang et al, 2011 ; Hastings et al, 2012 ; Li et al, 2017 ; Scott et al, 2018 ; Greaves et al, 2019 ). When compared to control participants, countermeasure exercises during the WISE-2005 study maintained HR, SV, and LVEDV and cardiac mass during HDBR ( Dorfman et al, 2007 ; Edgell et al, 2007 ), as did exercises without concomitant LBNP during a 70-day HDBR study at the NASA FARU facility (see description of exercises in lean body mass and muscle section) ( Scott et al, 2018 ).…”

High-Intensity Exercise Mitigates Cardiovascular Deconditioning During Long-Duration Bed Rest

“…Despite research spanning at least four decades on weightlessness-associated cardiovascular alterations (Pavy-Le Traon et al, 2007 ; Hargens and Vico, 2016 ), the exact time courses of changes in hemodynamic regulation and autonomic cardiovascular control induced by long-term spaceflight are not fully understood (Liu et al, 2015 ; Aubert et al, 2016 ). Moreover, several countermeasures for cardiovascular deconditioning have already been tested (e.g., volume loading, lower-body negative pressure, hypergravity; Wang et al, 2011 ; Stenger et al, 2012 ; Jeong et al, 2014 ; Li et al, 2017 ), but exercise is the most investigated countermeasure (Blaber et al, 2009 ; Petersen et al, 2016 ; Ploutz-Snyder, 2016 ). However, despite the consensus on physical activity as a countermeasure, the type and intensity of the exercise are undergoing further investigation.…”