The astronauts exercised on a cycle ergometer during flight. No specific exercise protocol was required. Heart rates were recorded every 15 seconds during exercise. The frequency and duration of in-flight exercise sessions was noted, and the intensity of the exercise was quantified as the percentage of age-predicted maximum heart rate achieved during a session.
Lower work rates were achieved on landing day because the target heart rates were reached sooner, ending the tests. The rate of oxygen consumption that corresponded to a given heart rate was lower after the flight than before. At 85% of predicted maximum heart rate, the decrement in oxygen consumption was nine percent for astronauts who exercised during flight for more than 20 minutes at least three times a week at more than 70% of their predicted maximum heart rate. The decrement was greater for astronauts who exercised less often or at lower intensities. It was 15% for astronauts who exercised more than three times a week but achieved lower heart rates, and 23% for astronauts who exercised less frequently. The decrease in oxygen consumption did not correlate with flight duration. Because the exercise tests were performed upright, both exercise deconditioning and orthostatic deconditioning would have contributed to the higher heart rates during exercise. In this way the tests were similar to an emergency egress from the Shuttle. The results showed that in-flight exercise can help to maintain postflight aerobic capacity and that the intensity of exercise is important. On the basis of this and other studies (see DSOs 476, 608, and 618), it was recommended that space crews exercise for more than 20 minutes at least three times a week at work rates that elicit 70% of maximum heart rates, but that the maximum heart rates should be determined in preflight maximum exercise tests rather than estimated by age.
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