Moore AD, Jr, Downs ME, Lee SMC, Feiveson AH, Knudsen P, Ploutz-Snyder L. Peak exercise oxygen uptake during and following long-duration spaceflight. This investigation was designed to measure aerobic capacity (V O2peak) during and after long-duration International Space Station (ISS) missions. Astronauts (9 males, 5 females: 49 Ϯ 5 yr, 77.2 Ϯ 15.1 kg, 40.6 Ϯ 6.4 ml·kg Ϫ1 ·min Ϫ1 [mean Ϯ SD]) performed peak cycle tests ϳ90 days before flight, 15 days after launch, every ϳ30 days in-flight, and

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... n recovery days 1 (R ϩ 1), R ϩ 10, and R ϩ 30. Expired metabolic gas fractions, ventilation, and heart rate (HR) were measured. Data were analyzed using mixed-model linear regression. The main findings of this study were that V O2peak decreased early in-flight (ϳ17%) then gradually increased during flight but never returned to preflight levels. V O2peak was lower on R ϩ 1 and R ϩ 10 than preflight but recovered by R ϩ 30. Peak HR was not different from preflight at any time during or following flight. A sustained decrease in V O2peak during and/or early postflight was not a universal finding in this study, since seven astronauts were able to attain their preflight V O2peak levels either at some time during flight or on R ϩ 1. Four of these astronauts performed in-flight exercise at higher intensities compared with those who experienced a decline in V O2peak, and three had low aerobic capacities before flight. These data indicate that, while V O2peak may be difficult to maintain during long-duration ISS missions, aerobic deconditioning is not an inevitable consequence of long-duration spaceflight. Address for reprint requests and other correspondence: M. E. Downs, Values are based on the mixed-model linear regression analyses (estimated means Ϯ SE). FD, days after launch; R, recovery day; HR, heart rate; V E, ventillation; RER, respiratory exchange ratio. *Significantly different from preflight at an overall test level of 0.05 after adjustment for multiple comparisons. 233 Peak Oxygen Uptake and Long-Duration Spaceflight • Moore AD et al.