Effect of standing or walking on physiological changes induced by head down bed rest: implications for spaceflight
Vernikos, J.; Ludwig, D.A.; Ertl, A.C.; Wade, C.E.; Keil, L.; O'Hara, D.; Vernikos, J.; Wade, C.E.
Aviation Space and Environmental Medicine 67(11): 1069-1079
1996
ISSN/ISBN: 0095-6562 PMID: 8908346 Document Number: 455575
Background/Hypothesis: To simulate exposure to microgravity and to determine the effectiveness of intermittent exposure to passive and active +1 Gz force (head-to-foot) in preventing head-down bed rest (HDBR) deconditioning, 4 d of 6 degree HDBR were used. Methods: Volunteers were 9 males, 30-50 yr, who performed periodic standing or controlled walking for 2 or 4 h cntdot d-1 in 15-min bouts, one bout per hour, or remained in a continuous HDBR control condition (0 Gz). Results: Standing 4 h (S4) completely prevented, and standing 2 h (S2) partially prevented, decreases in post-HDBR orthostatic tolerance (survival rates with 30 min of upright tilt at 60 degree ). Walking, both 2 h (W2) and 4 h (W4), and S4 attenuated decreases in peak oxygen uptake compared to 0 Gz. Compared to 0 Gz, both 54 and W4 attenuated plasma volume loss during HDBR. Urinary Ca-2+ excretion increased over time with HDBR; the quadratic trend for urinary Ca-2+, however, was attenuated with W2 and W4. Conclusions: We concluded that various physiological systems benefit differentially from passive +1 Gz or activity in +1 Gz and, in addition to the duration of the stimulus, the number of exposures to postural stimuli may be an important moderating factor.