Inflight exercise affects stand test responses after space flight

Purpose: The purpose of this study was to determine whether exercise perfor med by Space Shuttle crew members during short-duration space flights (9-16 d) affects the heart rate (HR) and blood pressure (BP) responses to standi ng within 2-4 h of landing, Methods: Thirty crew members performed self-selected inflight exercise and maintained exercise logs to monitor their exercise intensity and duration. Two subjects participated in this investigation during two different flight s. A 10-min stand test, preceded by at least 6 min of quiet supine rest, wa s completed 10-15 d before launch (PRE) and within 4 h of landing (POST). B ased upon their inflight exercise records, subjects were grouped as either high (HIex: greater than or equal to 3 times/week, HR greater than or equal to 70% HRmax greater than or equal to 20 min/session, N = 11), medium (MED ex: greater than or equal to 3 times/week, HR greater than or equal to 70% HRmax greater than or equal to 20 min/session, N = 10), or low (LOex: great er than or equal to 3 times/week, HR and duration variable, N = 11) exercis ers. HR and BP responses to standing were compared between groups (ANOVA, P less than or equal to 0.05). Results: There were no PRE differences between the groups in supine or stan ding HR and BP. Although POST supine HR was similar to PRE, all groups had an increased standing HR compared with PRE. The increase in HR upon standin g was significantly greater after flight in the LOex group (36 +/- 5 bpm) c ompared with HIex or MEDex groups (25 +/- 1 bpm; 22 +/- 2 bpm). Similarly, the decrease in pulse pressure (PP) from supine to standing was unchanged a fter space flight in the MEDex and HIex goups but was significantly greater in the LOex group (PRE: -9 +/- 3; POST: -19 +/- 4 mm Hg). Conclusions: Thus, moderate to high levels of inflight exercise attenuated HR and PP responses to standing after space flight.