Effect of Simulated Microgravity and Lunar Gravity on Human Inspiratory Muscle Function: ‘Selena-T’ 2015 Study
As a part of the multi-disciplinary “SELENA-T”-2015 Bed Rest Study, we investigated the pattern of inspiratory muscles fatigue in 22 healthy male subjects during incremental exercise test to exhaustion before and after 21 days of hypokinesia evoked by bed rest. Hypokinesia consisted of head-down bed rest (HDBR) at a minus 6° angle, simulating microgravity present on orbiting spacecraft, in 10 subjects. The remaining 12 subjects spent the first 5 days of hypokinesia in HDBR position and the subsequent 16 days in head-up bed rest (HUBR) at a plus 9.6° angle, as a presumed analog of lunar gravity that is six times less than Earth’s gravity. Maximal inspiratory pressure (MIP) and electromyograms (EMG) of the diaphragm (D), parasternal (PS), sternocleidomastoid (SCM), and scalene (S) muscles served as indices of inspiratory muscle function. Before both HDBR and HUBR, exercise decreased MIP and centroid frequency (fc) of EMG (D, PS, SCM, and S) power spectrum (p < 0.05). After 3 weeks of HDBR, but not HUBR, inspiratory muscles fatigue was more expressed compared with control (p < 0.05). We conclude that HDBR lowers inspiratory muscles resistance to fatigue during high-intensity exercise while HUBR has no such effect. These changes may limit maximal ventilation and may contribute to exercise intolerance observed after prolonged simulated microgravity. The physiological mechanisms of respiratory muscle dysfunction after HDBR consist primarily of postural effects, and are not due only to hypokinesia.
KeywordsDiaphragm Exercise Fatigue Head-down bed rest Head-up bed rest Hypokinesia Parasternal Scalene Sternocleidomastoid
We thank the subjects for participating in «SELENA-T» Bed Rest Study and the nursing staff of the Federal Research and Clinical Center as well as the study team of Research Institute for Space Medicine for supervising the protocol of this investigation. The study was funded by the Federal Biomedical Agency of Russia.
Conflicts of Interest
No conflicts of interest, financial or otherwise, are declared by the authors.
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