Lower-body negative-pressure exercise and bed-rest-mediated orthostatic intolerance.
OBJECTIVE
Supine, moderate exercise is ineffective in maintaining orthostatic tolerance after bed rest (BR). Our purpose was to test the hypothesis that adding an orthostatic stress during exercise would maintain orthostatic function after BR.


METHODS
Seven healthy men completed duplicate 15-d 6 degrees head-down tilt BR using a crossover design. During one BR, subjects did not exercise (CON). During another BR, subjects exercised for 40 min.d(-1) on a supine treadmill against 50-60 mm Hg LBNP (EX). Exercise training consisted of an interval exercise protocol of 2- to 3-min intervals alternating between 41 and 65% (.)VO(2max). Before and after BR, an LBNP tolerance test was performed in which the LBNP chamber was decompressed in 10-mm Hg stages every 3 min until presyncope.


RESULTS
LBNP tolerance, as assessed by the cumulative stress index (CSI) decreased after BR in both the CON (830 +/- 144, pre-BR vs 524 +/- 56 mm Hg.min, post-BR) and the EX (949 +/- 118 pre-BR vs 560 +/- 44 mm Hg.min, post-BR) conditions. However, subtolerance (0 to -50 mm Hg LBNP) heart rates were lower and systolic blood pressures were better maintained after BR in the EX condition compared with CON.


CONCLUSIONS
Moderate exercise performed against LBNP simulating an upright 1-g environment failed to protect orthostatic tolerance after 15 d of BR.
Schneider
Suzanne M
SM
Department of Human Performance and Development, University of New Mexico, Johnson Center, Room 126, Albuquerque, NM 87131, USA. sschneid@unm.edu
Watenpaugh
Donald E
DE
Lee
Stuart M C
SM
Ertl
Andrew C
AC
Williams
W Jon
WJ
Ballard
Richard E
RE
Hargens
Alan R
AR
D000328:Adult; D000704:Analysis of Variance; D001510:Bed Rest; D001696:Biomechanical Phenomena; D002395:Catecholamines / Q000097:blood; D018592:Cross-Over Studies; D015444:Exercise / Q000502:physiology*; D006112:Gravitation; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D010809:Physical Fitness; D016683:Supine Position; D014893:Weightlessness
D002395:Catecholamines