How do you weightlift in a weightless environment? It’s an important question for astronauts on the International Space Station because the average ISS stay is six months, and in zero gravity it’s easy to move about and move things, so muscles do much less work than they do back on Earth. Without resistance exercise, muscles deteriorate and bones lose density. But a barbell or dumbbell is going to float just like the astronauts do. And even a weight stack on a machine will lack the Earth’s gravitational pull. The solution to weight-training in space is a very unique machine.


The Advanced Resistance Exercise Device (ARED) was installed on the International Space Station in January 2009, replacing the inefficient Interim Resistance Exercise Device (IRED). With the ARED, resistance is generated by two piston cylinder assemblies with an adjustable load that can provide up to 600 pounds (272 kg.) of resistance with the bar (double the resistance of the IRED) and up to 150 pounds (68 kg.) with the cable attachment. A flywheel mimics the force of free weights on cable exercises. To maintain muscle mass and bone density, astronauts on the ISS from various countries are encouraged to train two hours daily: weights and cardio. With the ARED, they can perform 29 different weight-training exercises, hitting every bodypart. Exercises include deadlifts, squats, bench presses, calf raises, crunches, military presses, upright rows, biceps curls, and triceps extensions.

Advanced Resistance Exercise Device
NASA astronaut Kjell Lindgren deadlifts in space with the ARED. / NASA

Space station astronauts strap themselves down to the removable bench for lying and seated exercises, but during standing exercises, like deadlifts and squats, hands on the bar and feet on the footpad keep them secure. And as for the ARED, it’s attached to the space station with a system of springs, dampers, and shock absorbers to limit forces transmitted to the ISS by an exercising astronaut. So, 600-pound deads aren’t going to rock the space station. NASA astronaut Doug Wheelock says of the ARED: “We can adjust the loading here by this cranking lever, and then we can go from zero to 600 pounds, so it’s plenty [of resistance] to reach any bit of loading that you can even imagine on this bar and the cable as well.”

Wheelock demonstrated the ARED with squats and bench presses in this NASA video:

“When we think about the space environment, you have to reset the baseline,” Scott Trappe, director of Ball State University’s Human Performance Laboratory told Wired magazine. “On Earth, it’s hypertrophy: ‘How big can I get my muscles?’ In space, it’s ‘How can I protect what I have?'” Floating around in near-zero gravity is the equivalent of lying in a bed for months when sick. Muscles atrophy from non-use when they’re not even doing the little, repetitive things like keeping us upright or propelling us forward when walking. By working all bodyparts and allowing astronauts to go heavy on standing, compound exercises—squats and deadlifts—the ARED is the pro-gravity solution to anti-gravity.


A major feature of ARED is the monitoring and prescriptive advice system, which is like a computerized sports scientist. NASA says: “This system includes triaxial force sensors located in the exercise platform that are able to record force in three dimensions. In addition, load sensors in the main lift arm and the arm base assembly measure unidirectional forces. The arm base assembly also has rotational sensors that record the range of motion of the arm.” During the workout, this data is transmitted to the Mission Control Center at Johnson Space Center (Houston) and the exerciser’s history, progress, and prescription for workout progress is transmitted back to the ARED tablet PC, recommending which exercises, resistance, and rep targets will garner the best results.

As is often is the case, space exploration is leading technological advances. In this case, we may be getting a glimpse of future, long-range, space travel when astronauts can stay fit for years without gravity. But we’re also seeing the not-to-distant future of workout monitors and virtual sport scientists, maybe coming to your gym, right here on Earth.