When you think about what it’s like to live in space, you might imagine the stunning views of Earth or the existential wonder of being out among the stars. What you might not consider are some of the practicalities, like working out. We all know we’re supposed to go to the gym regularly, but that’s easier said than done when you live on a space station.
And exercise is important — even more so for astronauts than the rest of us. That’s because arguably the biggest challenge for human health in space is something that’s missing: gravity. The International Space Station (ISS) has what is called a microgravity environment (because it’s not quite technically zero gravity, though in practice, it’s close enough). Without the force of gravity acting on their bodies, astronauts can float and spin through the air, but that means their muscles aren’t working to hold them up as they usually would be on Earth.
Over time, this lack of gravity can have serious health effects. Muscle and bone mass drop due to a lack of use, which could be disastrous when the astronauts return to Earth and have to deal with normal gravity conditions once more. Microgravity can have other effects too, including on the cardiovascular system.
So, it’s vitally important for astronauts to exercise regularly to work against those microgravity effects. You might have heard that astronauts spend over two hours per day on exercise, and this is why — they need to pack in all the work on their muscles that most of us get throughout the day just from being upright, as well as stay fit and healthy for demanding jobs like spacewalks.
There are three main pieces of exercise equipment on the ISS currently in use: a treadmill, a stationary bicycle, and a resistance machine. In some ways, the exercises astronauts do aren’t so different from what you’d find in any gym on Earth — they run, they cycle, they lift weights.
But there are some technical challenges that come into play when you need to lift weights when there’s no gravity.
A machine called ARED, or Advanced Resistive Exercise Device, has a fixed bar that can be moved in various ways, a bit like a Smith Machine or squat rack. But instead of using weights for the resistance, it uses vacuum cylinders. The astronauts must work against the pull of this vacuum to move the bar, and they can vary the amount of resistance to simulate using heavier weights.
While the treadmill and the stationary bike work much as they would on Earth, there’s also a challenge with these — how to stop the astronauts from floating away when they run or push down on the pedals. To prevent this, they use harnesses to keep them tethered to the equipment, though the equipment also needs to be carefully designed to prevent the astronauts from producing vibrations as they work out that could damage the Space Station.
Bruce Nieschwitz, a specialist with the Astronaut Strength, Conditioning, and Rehabilitation group at NASA’s Johnson Space Center, says that exercise isn’t only important for astronauts’ physical health.
“The benefits of exercise are not just with bone, or muscle, or even cardiovascular training. It’s really a full-body, full-systems benefit,” Nieschwitz told Digital Trends. “We know just from studies on the ground that exercise will improve the mood, as well as helping with sleep and issues like that. It’s not just muscle strength and size that we’re worried about. We definitely want to encourage crewmembers to feel like 100% normal people, even in a very strange and not natural environment.”
As anyone who’s been going to the gym for a while knows, though, even the best equipment in the world won’t help if you don’t have a good program. The exercise programs for NASA astronauts are specially designed to focus on the most efficient way to overcome the deficits they’ll experience from their stay in space and to avoid injury. That’s particularly important for when astronauts return home to Earth, so that they’re better able to adjust to life with gravity.
“Exercise is the countermeasure to the microgravity world that they are living in,” Nieschwitz explained. “We’re trying to avoid the deficits that are going to be caused by the microgravity environment. So we want to stimulate the muscle, stimulate the bone, keep it as healthy as possible. So health is really the main focus of the exercise prescription.”
The team designs a program of both cardio and resistance exercises that most astronauts do six days per week. You’ll often hear that astronauts spend two-and-a-half hours each day exercising, but that’s not quite right: They have that much time allotted to exercising, but that includes setting up, getting ready, and putting everything away.
Typically, each astronaut will do around one hour of exercises using the ARED machine, then a further 30 to 40 minutes of cardio. That’s still a lot of time to be working out, but Nieschwitz says that it isn’t a problem to motivate the astronauts.
“Most crewmembers are very protective of the exercise time that they do in orbit,” Nieschwitz said.
When they feel most normal is when they’re doing their exercise.
Even those who aren’t avid gym rats still know the benefits of working out, for both their body and their mind. “I’ve heard different people describe it as when they feel most normal is when they’re doing their exercise,” Nieschwitz said, adding that it’s even more so than when they’re sleeping or eating. “They can get away from the other parts of their life on the space station that are work-related.”
The team programs a lot of multiple-joint compound exercises like squats and presses, because they’re an efficient way to work out multiple large muscles at the same time. They also use a variety of rep ranges, from low-rep strength-focused work to higher-rep endurance-focused work. The cardio can vary too, with higher-intensity shorter sessions or lower-intensity longer sessions.
Astronauts consider the effects of physically challenging work like spacewalks as well, with some crewmembers choosing to take days before or after spacewalks off from exercise to give their bodies a break, and some choosing to do extra work to improve grip strength, which can help them perform delicate operations in cumbersome gloves.
The astronauts have freedom to choose what exercises they want to do, but they generally follow the program. “They’re able to completely change things independently from us, but for the most part, they follow exactly what we want because they trust our team and we’ve been doing it a long time and we’ve had a lot of success with it,” Nieschwitz said.
The exercise machines on the ISS have been pretty well optimized by this point, and improvements tend to be incremental — such as a recent upgrade from a 350-watt bike to a 500-watt one.
In terms of further improvements in astronaut health in the future, researchers are looking to projects that might be able to support health in other ways, such as through recovery. A new project from the European Space Agency (ESA), for example, will be looking at the use of electrical muscle stimulation on astronauts on the space station.
Neuromuscular electrical stimulation (NMES) is mostly used on Earth for helping patients recover after events like a stroke, and has been tested on some professional sports players as a recovery aid. It’s not a replacement for exercise, but it might be useful in helping ease soreness after that exercise has been done.
When it comes to applying NMES in space, “[t]he principle is exactly the same,” compared to on the ground, said the PI of the research project, Alessandra Bosutti of the University of Trieste in Italy. “But the difference is in how we apply the protocols to the astronauts, because the astronauts are floating.”
Bosutti’s project uses a small device that astronauts will attach to their bodies after exercise to see if it aids their recovery. Over the next five to six years, they will take data from the astronauts before, during, and after their time in space and compare this to data from astronauts who don’t use the device.
“The idea is that this system could help make recovery faster when astronauts arrive back on Earth after the mission,” Bosutti explained.
They are particularly interested in the later periods of time the astronauts spend on the station, when they have been there for a while and have likely lost some muscle. The researchers want to test whether interventions like NMES can help astronauts maintain strength and muscle mass, which is particularly important for longer-term missions.
Looking ahead to longer missions like theoretical crewed missions to Mars, astronauts will be away from Earth for longer than ever. And they will have a very limited amount of space to work out, with only a small amount of weight that can be carried with them.
“We need smaller equipment, lighter equipment, easy to use equipment, and efficient equipment,” said Inês Antunes, human research lead support at Telespazio for the European Space Agency (ESA). “Something like muscle stimulation is passive, and would fit in a small, confined mission.”
ESA is looking into interventions as varied as having participants work out while in centrifuge-like artificial gravity machines, or using meditation-like audio recordings to help astronauts relax, all in the hopes of reducing the punishing effects of spaceflight on the human body.
And beyond the human body, researchers are looking to optimize the environments in which the astronauts will operate, all in the name of health. “Even simple things like helping astronauts feel hungry, so that they don’t get energy loss,” Antunes said. “Things like having food be more crunchy, or having a setting to eat that is more pleasant, will help them eat better.”
Much of this research covers not just exercise, but also nutrition, supplements, and passive interventions like muscle stimulation — and seeing how these different interventions all interact with each other.
“We can never study one body system individually,” Antunes said, as any comprehensive research has to consider the body as a whole, including everything from cardiovascular systems to nutrition to mental health. “These all work together. If someone is not OK mentally, it will affect their immune system. And if their immune system is not well, it will affect the muscles.”