We have to know that most astronauts lose their one to 2% of their bone mass per month in zero-G in the space ship. And to slow down the bone loss problem, the ISS was recently shipped an advanced Resistive Exercise Device called aRED. This machine is constructed with a vacuum cylinders system which can be use by astronauts for exercises. There is several exercises offers that has a workloads up to 600 pounds. An astronaut will can run on a treadmill and/or bicycle up to two hours a day in space.