A person who is inactive for an extended period of time (such as when they have a long illness) loses strength as well as muscle and bone mass. Astronauts on the International Space Station (ISS) face similar risks because bones and muscles begin to atrophy in the absence of gravity. Resistive exercise, where the musculoskeletal system bears weight, has been shown to mitigate these effects. But just lifting weights, as we do on Earth, does not work without gravity.
Engineers at NASA Johnson developed a special resistive exercise device for astronauts on the ISS to follow a personalized exercise plan in the microgravity environment of low-earth orbit. The Advanced Resistive Exercise Device (ARED) has the capability to exercise all major muscle groups — focusing on squats, dead lifts, and calf raises — and helps the crew maintain their strength and endurance.
The ARED is a mechanically simple but robust device. It employs vacuum cylinders to provide a constant resistance, while flywheel assemblies provide a variable resistance. The variable resistance supplied by the flywheel assemblies is designed to mimic the inertial forces generated when lifting free weights on Earth. It is not dependent on gravity to operate but can operate in Earth gravity as well as microgravity.
It was flown to the ISS in November 2008 and is designed to last at least 15 years, with a total life of more than 11.2 million cycles. The ARED accommodates a wide range of body types and sizes. There is also a touchscreen that makes it easier for an astronaut to follow a personalized prescribed exercise plan. A crewmember may select any exercise from their prescription or choose other available exercises. The crew performs their exercises using either a lift bar or a cable assembly. Resistive load can be adjusted between 0 and 600+ pounds for bar-related exercises and up to 150 pounds for cable-related exercises.