Key result
Moderate exercise performed against LBNP simulating an upright 1-g environment failed to protect orthostatic tolerance after 15 days of bed rest compared to no exercise.
Why the study?
Does moderate exercise against lower-body negative-pressure prevent orthostatic intolerance in healthy men undergoing 15-day bed rest?
RCT (n=7)
Does moderate exercise against lower-body negative-pressure prevent orthostatic intolerance in healthy men undergoing 15-day bed rest?
Moderate supine exercise against lower-body negative pressure does not prevent the decline in orthostatic tolerance induced by 15 days of bed rest.
Answers are grounded in this paper and cite their sources.
Moderate LBNP exercise fails to prevent orthostatic intolerance after bed rest; leaves open effective countermeasures for deconditioning.
PURPOSE: 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. CONCLUSION: Moderate exercise performed against LBNP simulating an upright 1-g environment failed to protect orthostatic tolerance after 15 d of BR.
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Schneider et al. (2002) conducted an RCT in Bed-rest mediated orthostatic intolerance (n=7). Exercise on a supine treadmill against 50-60 mm Hg LBNP vs. No exercise during bed rest was evaluated on LBNP tolerance assessed by cumulative stress index (CSI). Moderate exercise performed against LBNP simulating an upright 1-g environment failed to protect orthostatic tolerance after 15 days of bed rest compared to no exercise.
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