OXYGEN UPTAKE DURING SUBMAXIMAL AND MAXIMAL CYCLING BEFORE, DURING AND AFTER SPACEFLIGHT 1083

Abstract

In an effort to determine the influence of a 17 day exposure to spaceflight on cardiorespiratory function during exercise, we studied four male crew members of the Life & Microgravity Science mission aboard the STS-78 Space Shuttle flight. Measurements of oxygen uptake, pulmonary ventilation, and heart rate were made during submaximal supine cycling (100, 150, 175 w) 30 and 15 d (L-30 & L-15) prior to lift-off, on flight days 3, 9, and 13 (F3, F9,& F13), and on days 1, 4, and 8 (R1, R4, R5&R8) after return to earth. In addition, maximal oxygen uptake (VO2 max) measurements were made at L-15, R4, and R8. Maximal workloads on days L-30, F3, F8, F13, R1 and R5 were limited to 85% VO2 max. Based on submaximal VO2 and maximal heart rate(avg=181 bts/min) for each crew member, oxygen uptake at maximal heart rate(VO2 @ HRmax) was calculated. These values were highly correlated with VO2 max(r=0.91). Though oxygen uptake (1/min) during the submaximal exercise was unaffected by spaceflight, heart rates were elevated, on average, 5 bts/min during in-flight testing, and 9-10 bts on R1, but returned to the pre-flight values by R5. VO2 max decreased by 10.3% from L-15 to R4, returning to normal by R8. VO2 @ HRmax showed a continued decline throughout the flight, reaching a nadir of -15.7% during testing on F13, which returned to the pre-flight level by R5. These changes in VO2 @ HRmax and VO2 max appear, in part, to be associated with a decline in total body water, as reflected by their loss of body weight during the adaptation to spaceflight and rehydration during the days following their return to earth.