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Effect of orthostatic stress on exercise performance after bed rest

, : Effect of orthostatic stress on exercise performance after bed rest. Aviation Space & Environmental Medicine 53(7): 652-657

The cardiorespiratory repsonses to supine against upright exercise were compared to determine the orthostatic effects of gravity on exercise performance following bedrest (BR) [a simulation of weightlessness]. Five healthy male subjects underwent 7 days of continuous BR. Two days prior to BR (pre-BR) each subject performed a submaximal exercise test in the supine position consisting of 5 min rest, 5 min exercise at 700 kgm/min and with 10 min of recovery from exercise. After the subject's heart rate (HR) returned to within 5 bpm of the pre-exercise value, the submaximal test was repeated in the upright position. Systolic (SBP) and diastolic (DBP) blood pressures, HR, O2 uptake (.ovrhdot.VO2), and ventilation volume (.ovrhdot.VE) were measured during each 30 s of all exercise tests. Supine and upright submaximal exercise tests were repeated on the day following BR (post-BR). The subjects showed significant increases (P < 0.05) in post-BR .ovrhdot.VE during supine and upright exercise and recovery from exercise. During rest and exercise, post-BR .ovrhdot.VO2 was not different from the pre-BR values for both tests. However, recovery .ovrhdot.VO2 following post-BR upright exercise was greater than the pre-BR vaue (+8.1%, P < 0.05) while supine recovery .ovrhdot.VO2 did not change. Compared to pre-BR, upright resting HR was elevated (P < 0.05) following BR. During supine exercise and recovery, mean HR increased by 3.8% and 5.9%, repectively (P < 0.05) post-BR, while exercise and recovery HR increased to a greater degree (P < 0.05) in the upright position. Compared to pre-BR values, post-BR heart rate-pressure-product (RPP) increased more (P < 0.05) during upright rest, exercise and recovery compared to corresponding supine values. During the post-BR upright test, pulse pressure (PP) and O2 pulse decreased in both tests compared to pre-BR values, with consistently larger changes observed in the upright position. There is apparently an orthostatic effect on work performance following BR deconditioning in addition to the effects caused by decreased physical activity.


PMID: 7115253

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