Question: how long does an average person need to exercise a day?

Jonathan Scott answered on 7 Oct 2015:

For health on Earth, the current recommendation is 5 sessions of moderate intensity exercise lasting at least 30 min. However, we know that doing just one bout of exercise a week can make a big difference if someone does not currently do any, so 5 times a week is the target, but if this isn’t possible, something is better than nothing.

For space, we don’t yet know how much you need. Currently astronauts exercise about 10 times per week, with a combination of aerobic exercise (treadmill running, cycling) in 30 min bouts, and resistance exercise, using a weight-lifting machine. The most recent research from the space station shows that this exercise program is effective at preventing the loss of muscle and bone strength, and physical fitness, that normally occurs in space. However, this exercise program requires three (large and complicated) exercise devices and takes a lot of time, so it is not ideal for space flight. Another question is whether we actually need to completely prevent these changes from happening and could we accept small decreases if this meant we didn’t need so much equipment and time – if we want to explore deep into space, we will not have a vehicle the size of the space station, so we will need to design some clever new exercise devices that are much smaller and simpler, but can still be effective.