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Lower body negative pressure exercise plus brief postexercise lower body negative pressure improve post-bed rest orthostatic tolerance

¹Department of Integrative Physiology, University of North Texas Health Science Center, Fort Worth, Texas; ²Department of Community Health Sciences, Brock University, St. Catharines, Ontario, Canada; ³University of New Mexico, Albuquerque, New Mexico; ⁴Wyle Laboratories, Houston, Texas; ⁵Department of Orthopaedic Surgery, University of California, San Diego, California; ⁶Department of Physiology, Gifu University, Gifu, Japan; and ⁷University of Waterloo, Waterloo, Ontario, Canada

Submitted 7 January 2007 ; accepted in final form 12 October 2007

Orthostatic intolerance follows actual weightlessness and weightlessness simulated by bed rest. Orthostasis immediately after acute exercise imposes greater cardiovascular stress than orthostasis without prior exercise. We hypothesized that 5 min/day of simulated orthostasis [supine lower body negative pressure (LBNP)] immediately following LBNP exercise maintains orthostatic tolerance during bed rest. Identical twins (14 women, 16 men) underwent 30 days of 6° head-down tilt bed rest. One of each pair was randomly selected as a control, and their sibling performed 40 min/day of treadmill exercise while supine in 53 mmHg (SD 4) [7.05 kPa (SD 0.50)] LBNP. LBNP continued for 5 min after exercise stopped. Head-up tilt at 60° plus graded LBNP assessed orthostatic tolerance before and after bed rest. Hemodynamic measurements accompanied these tests. Bed rest decreased orthostatic tolerance time to a greater extent in control [34% (SD 10)] than in countermeasure subjects [13% (SD 20); P < 0.004]. Controls exhibited cardiac stroke volume reduction and relative cardioacceleration typically seen after bed rest, yet no such changes occurred in the countermeasure group. These findings demonstrate that 40 min/day of supine LBNP treadmill exercise followed immediately by 5 min of resting LBNP attenuates, but does not fully prevent, the orthostatic intolerance associated with 30 days of bed rest. We speculate that longer postexercise LBNP may improve results. Together with our earlier related studies, these ground-based results support spaceflight evaluation of postexercise orthostatic stress as a time-efficient countermeasure against postflight orthostatic intolerance.

human; microgravity; spaceflight; countermeasure; cerebral blood flow

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				S. M. C. Lee, S. M. Schneider, W. L. Boda, D. E. Watenpaugh, B. R. Macias, R. S. Meyer, and A. R. Hargens LBNP exercise protects aerobic capacity and sprint speed of female twins during 30 days of bed rest J Appl Physiol, March 1, 2009; 106(3): 919 - 928. [Abstract] [Full Text] [PDF]