Physical Activity in Space

Everyone knows that it's important to exercise to stay in shape—on Earth, that is. But when you're in orbit, exercise is absolutely vital!

Physical activity is the most effective way to counteract the adverse effects of weightlessness on the human body. Exercise is therefore a crucial part of the daily routine on board the International Space Station (ISS). Over the course of a long-duration mission, astronauts must exercise approximately two hours per day!

Canadian astronaut Bob Thirsk

Former Canadian astronaut Robert Thirsk enjoys cycling on board the ISS! (Credit: NASA)

The importance of physical activity in orbit

That means that without exercise, the astronauts' bones would be more fragile and their muscles weaker after time spent in space.

On Earth, each time we move, gravity provides resistance to the muscles and bones of our body. It's like we're exercising without even realizing it! That way, our body stays strong enough to support our weight.

In microgravity, however, bones and muscles no longer have to support the weight of astronauts' bodies. What's more, the cardiovascular system becomes lazy because the heart doesn't have to work as hard as it does on Earth to counteract gravity and pump blood up to the head.

If astronauts didn't exercise while they were in space, their bodies would experience major loss in:

In other words, astronauts need to stay in shape in order to:

  • mitigate the deterioration of their bones
  • maintain the strength of their muscles and their heart
  • remain strong enough to do spacewalks
  • be able to carry out emergency procedures during landing
  • stay healthy and in shape until they return to Earth and to gravity

Space gym

Exercising looks a bit different in microgravity. Exercise machines have been modified to simulate a gravitational pull being exerted on the astronauts' bodies.

The team members on the ISS use three cardiovascular and muscular exercise machines to stay in shape.

ARED: Advanced Resistive Exercise Device

Bob Thirsk - ARED

  • Type of exercise: Maintains muscle strength and bone density by targeting the major muscle groups.
  • Special features: This device uses vacuum cylinders. They exert up to 272 kilos of resistance on a bar or cable. The device imitates free weights used on Earth.
  • Method of use:
    1. Grasp the exercise bar firmly.
    2. Adjust the resistance to the desired level.
    3. Perform heel lifts, squats and deadlifts, depending on the muscles to be worked.


Bob Thirsk - TVIS

During his six-month mission on the ISS, Robert Thirsk ran "alongside" his son!

He used videos filmed by the Canadian Space Agency (CSA) that showed his son running. Robert watched the videos on the treadmill's screen, and the illusion was complete!

  • Type of exercise: Cardiovascular, muscular and skeletal.
  • Special features: The bungee and harness apply a load to the shoulders and hips based on the astronaut's body weight. At the start of a mission, the load is set at 60% of the astronaut's body weight. The load is increased throughout the mission until it is at 85% to 100% of the weight.
  • Method of use:
    1. Put on the harness system.
    2. Adjust the load of the harness based on the desired intensity of the workout.
    3. Run!

Stationary bike

Bob Thirsk - CVIS

  • Type of exercise: Cardiovascular.
  • Method of use :
    1. Place feet on the clip pedals.
    2. Put on the back harness to remain secured to the machine.
    3. Grasp the hand holds to maintain balance on the machine.
    4. Pedal!

Side effects of weightlessness on the human body

Flying in space is a bit like aging prematurely.

Chris Hadfield undergoes CT scan

Chris Hadfield undergoes a quantitative CT scan to obtain detailed images of the bones in his ankle, shortly after his return to Earth in 2013. (Credit: CSA)

Despite a rigorous exercise regime, astronauts lose an average of 1% of their bone density per month in space. On Earth, an average elderly person loses 1% of his or her bone density per year.

Thanks to the current protocol of two hours of exercise per day, astronauts return to Earth with more muscle mass than when they blasted off!

The physical consequences of a prolonged journey in weightlessness are similar to those caused by osteoporosis, which affects elderly people. However, these consequences aren't as serious because astronauts' bone density gradually returns to normal after they return to Earth.

That is why scientists use astronauts as subjects in their scientific experiments. This research allows us to gain a better understanding of the effects of weightlessness and how to mitigate them, for the purposes of future long-duration space missions but also for people with various health problems on Earth.

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