In this clip from September 2012, US astronaut Sunita Williams on board the ISS simulates taking part in a triathlon by “swimming”, biking and running the same distances as the real event. After “swimming” half a mile, biking 18 miles and finally running 4 miles, Williams finished in a very respectable time of 1 hour, 48 minutes and 33 seconds - which says a lot for her overall fitness condition.
The ISS has its own treadmill and stationary bike that use harnesses and straps to hold you in place, as otherwise you would simply float away! The swimming activity of the race was simulated by using the
Advanced Resistive Exercise Device (ARED) to do resistance exercises - not quite swimming but as close as you will get in Space.
Exercise is mandatory for all astronauts in a microgravity environment as muscle and bone deterioration is a serious problem. This becomes more of an issue the longer the period of 'weightlessness' and is a
major consideration for any long duration spaceflight. A mission to planet Mars, for example, would have a flight time of anywhere between 150-300 days depending on factors such as launch speed and the alignment of Earth and Mars.
So - how do you persuade astronauts to adhere to a strict daily exercise plan of 2 hours exercise a day- 7 days a week? This is one of the many problems that will need to be addressed. Experience of astronaut behaviour to date tells us that motivation to exercise is often lacking - they are human after all!