The preservation of astronauts’ aerobic capacity is a major goal of exercise countermeasures during space missions.
As one of the parameters indicating exercise capacity and indirectly of endurance, maximal oxygen uptake during exhaustive exercise, the VO2 max, is measured. As exhaustive exercise is not under all conditions what you want to do on orbit, an alternative is to check changes in oxygen transport at a certain heart rate.
Reduced oxygen uptake relative to the earlier measurement will then indicate a deterioration or the opposite in work capacity. The protocol uses a stair-case step function, pre-programmed into the exercise ergometer, so that you exercise for a fixed time on a certain level, and then step up to next level.
German Sport University (Deutsche Sporthochschule), Germany.