VO2max is the standard measure of aerobic capacity and is directly related to the physical working capacity of an individual. The VO2max of an individual is affected by uptake of oxygen in the lungs, extraction of oxygen from the arterial circulation by working muscles and by cardiac output. Aerobic deconditioning causes a lowering of VO2max which results in a diminished capacity to perform strenuous physical tasks. Heart rate data previously collected during cycle exercise tests onboard the ISS indicate that VO2max is likely lowered during and following flight; however, actual measurements of VO2max have not been made during long-duration space flight.
The European Space Agency (ESA) provided Portable Pulmonary Function System (PPFS), which was used to measure the oxygen uptake, cardiac output, heart rate, and blood pressure responses of the astronaut participants when performing a cycle exercise test at submaximal, maximal, and peak levels. The maximal exercise tests conducted during flight occurred during portions of the ISS orbit suitable for real-time downlink of single lead electrocardiograph data.
During baseline data collections, the subjects underwent a peak cycle test. During this test, a standard commercial off the shelf metabolic gas analysis system was used. The early preflight test results were used to define the exercise protocol used for subsequent pre- and postflight testing conducted during baseline data collection. During these tests, the crewmember performed a modified exercise protocol consisting of 5 minute stages at workloads eliciting 25, 50, and 75% of their preflight aerobic capacity test, followed by a 25 watt increase in workload every minute until the subject reached their maximum exercise capacity. During these tests heart rate (ECG), blood pressure, workload, perception of effort, metabolic gas exchange, and cardiac output were measured using the PPFS hardware.
The In-flight protocol was conducted on flight day 15 and every 30 days. Prior to performing the exercise test, the PPFS’s gas analyzer and respiratory volume measurement components were calibrated. During the test, the crewmember exercised on the cycle ergometer, inhaling cabin air and expiring through a mouthpiece; the nostrils were occluded with a nose clip. Expired breath was collected for metabolic gas analysis. Blood pressure was measured at automatically designated time intervals throughout the protocol. Cardiac output measurements were performed using a non-invasive rebreathing technique prior to exercise and during the last minute of the first three exercise stages. The electrical signals of the heart were measured using electrodes placed on the skin. Once the protocol has been completed, the PPFS was powered down and the sub-instruments were disconnected and stowed.
The main findings of this study were that VO2peak decreased early in-flight then gradually increased during flight but never returned to preflight levels. VO2peak was lower on R+1 and R+10 than preflight but recovered by R+30. Peak heart rate was not different from preflight at any time during or following flight. A sustained decrease in VO2peak during and/or early postflight was not a universal finding in this study, since seven astronauts were able to attain their preflight VO2peak levels either at some time during flight or on R+1. Four of these astronauts performed in-flight exercise at higher intensities compared with those who experienced a decline in VO2peak, and three had low aerobic capacities before flight. These data indicate that, while VO2peak may be difficult to maintain during long-duration ISS missions, aerobic deconditioning is not an inevitable consequence of long-duration space flight.
|Mission||Launch/Start Date||Landing/End Date||Duration|
|Expedition 20||05/27/2009||10/11/2009||137 days|
|Expedition 21||10/11/2009||12/01/2009||51 days|
|Expedition 22||11/30/2009||03/18/2010||109 days|
|Expedition 23||03/18/2010||06/01/2010||75 days|
|Expedition 24||06/01/2010||09/25/2010||117 days|
|Expedition 25||09/24/2010||11/25/2010||31 days|
|Expedition 26||11/26/2010||03/16/2011||111 days|
|Expedition 27||03/14/2011||05/23/2011||70 days|
|Expedition 28||05/23/2011||09/15/2011||115 days|
|Expedition 29||09/16/2011||11/21/2011||40 days|
|Expedition 30||11/14/2011||04/27/2012||166 days|
|Expedition 31||04/27/2012||07/01/2012||65 days|
|Expedition 32||07/01/2012||09/16/2012||78 days|