F-12J Free Communication/Thematic Poster Space Flight and Bed Rest Deconditioning
During Skylab missions, a decrease in aerobic capacity was reported early in-flight with gradual recovery over the remainder of flight. To minimize any change in aerobic capacity throughout a mission, crewmembers onboard the International Space Station (ISS) are prescribed aerobic exercise on a cycle ergometer or treadmill six days a week during long duration space flight.
The objective of this study was to determine if aerobic capacity changes during long duration space flight onboard ISS.
ISS crewmembers (3 males, 1 female) performed a cycle ergometer test to determine peak oxygen uptake (VO2pk) and heart rate (HR) approximately 9 months prior to their missions. A Physical Fitness Evaluation (PFE) protocol (submaximal cycle test) was developed since maximal exercise testing was not permitted by the NASA-CPHS during flight. During the PFE, HR was measured during the last minute of each 5-minute stage of exercise at 25%, 50%, 75% and 25% of VO2pk. The PFE protocol was performed 2 months before launch (PRE) and at 40–65 days (FD 40–65), 90–100 days (FD 90–100) and 140–150 days (FD 140–150) of space flight. The HR and VO2 relation was determined for each subject and test session using linear regression. For the inflight tests it was assumed the VO2 per given workload was similar to preflight. The VO2 calculated to occur at peak HR for each test was used as a predictor of aerobic capacity. Estimated VO2pk was analyzed using a repeated measures ANOVA (p < .05) with Tukey's post-hoc comparisons.
A significant decrease in estimated VO2 was seen from PRE (3.60 ± 1.06 L/min, mean ± SD) to FD 40–65 (2.91 ± 0.68 L/min, p = .03). No statistical differences were seen between the PRE vs. FD 90–100 (3.11 ± 0.60 L/min, p = .13) and FD 140–150 (3.33 ± 0.83 L/min, p = .55).
During the early stages of an ISS mission there is a significant decline in aerobic capacity, but as the mission progresses aerobic capacity gradually increases to levels comparable to pre-flight.