Wired took a look at how it works.
Unlike the Bowflex’s rubber bands (which, coincidentally, were used by the machine being replaced, the iRED), the aRED uses piston-driven vacuum cylinders that provide adjustable resistance as the piston is pulled in or out. A flywheel system counteracts the force of the pistons to simulate the response of free weights in normal gravity.
While astronauts have been just fine with their cardio, studies detailing the damaging effects of muscle lost after a long-term space mission are still coming in. A recent report stated that without exercises like those possible on the aRED, astronauts could lose up to 15% of their muscle volume, which could be difficult or even impossible to regain back on earth. So the aRED’s goal is not to build muscle but simply to maintain it.
With a voyage to Mars expected to take at least six months, this is a problem that needs to be solved. Thankfully, the aRED is well on its way to keeping astronauts buffed enough for the job. [Wired Science]