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Measurements of oxygen uptake, pulmonary ventilation, and heart rate were made during submaximal cycling 60, 30, and 15 days before the SF liftoff and 12 and 7 days before BR; on SF days 2, 8, and 13 and on BR days 2, 8, and 13; and on days 1, 4, 5, and 8 after return to Earth and on days 3 and 7 after BR. During 15 days before liftoff, day 4 after return, and day 8 after return and all BR testing, each subject completed a continuous exercise test to volitional exhaustion on a semirecumbent (SF) or supine (BR) cycle ergometer to determine the submaximal and maximal cardiorespiratory responses to exercise. The remaining days of the SF testing were limited to a workload corresponding to 85% of the peak pre-SF peak oxygen uptake (V\u0307o<jats:sub>2 peak<\/jats:sub>) workload. Exposure to and recovery from SF and BR induced similar responses to submaximal exercise at 150 W. V\u0307o<jats:sub>2 peak<\/jats:sub>decreased by 10.4% from pre-SF (15 days before liftoff) to day 4 after return and 6.6% from pre-BR to day 3 after return, which was partially (SF: \u22125.2%) or fully (BR) restored within 1 wk of recovery. Workload corresponding to 85% of the peak pre-SF V\u0307o<jats:sub>2 peak<\/jats:sub>showed a rapid and continued decline throughout the flight (SF day 2, \u22126.2%; SF day 8, \u22129.0%), reaching a nadir of \u221211.3% during testing on SF day 13. During BR, V\u0307o<jats:sub>2 peak<\/jats:sub>also showed a decline from pre-BR (BR day 2, \u22127.3%; BR day 8, \u22127.1%; BR day 13, \u22129.0%). These results suggest that the onset of and recovery from real and simulated microgravity-induced cardiorespiratory deconditioning is relatively rapid, and head-down-tilt BR appears to be an appropriate model of this effect, both during and after SF.<\/jats:p>","DOI":"10.1152\/japplphysiol.01083.2005","type":"journal-article","created":{"date-parts":[[2005,11,24]],"date-time":"2005-11-24T01:44:38Z","timestamp":1132796678000},"page":"951-957","source":"Crossref","is-referenced-by-count":82,"title":["Cardiorespiratory responses to physical work during and following 17 days of bed rest and spaceflight"],"prefix":"10.1152","volume":"100","author":[{"given":"Todd","family":"Trappe","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Scott","family":"Trappe","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gary","family":"Lee","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jeffrey","family":"Widrick","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Robert","family":"Fitts","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"David","family":"Costill","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"24","reference":[{"key":"R1","doi-asserted-by":"publisher","DOI":"10.1152\/jappl.1996.81.1.98"},{"key":"R2","unstructured":"Astrand POand Rodahl K.Textbook of Work Physiology: Physiological Bases of Exercise.New York: McGraw-Hill, 1986."},{"key":"R3","doi-asserted-by":"publisher","DOI":"10.1139\/h94-003"},{"key":"R4","doi-asserted-by":"publisher","DOI":"10.1161\/01.CIR.65.1.134"},{"key":"R5","unstructured":"Convertino VA.Exercise and adaptation to microgravity environments. 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