Astronaut Illustration

Out of this world

Long-term low gravity can seriously affect us

When we move around in low or zero gravity, the mechanical strain applied to our skeleton is much lower than on Earth. This is why moving around in low-gravity environments, such as space, gradually depletes bone mass. Muscle atrophy (wasting) is also a problem and begins even on short missions (see our ‘Wasting away’ article).

Crew on the International Space Station (ISS) can spend six months in orbit and have to exercise for hours every day on special equipment to reduce muscle loss; they also have to follow an exercise programme when they return to Earth. A human mission to Mars would take almost a year – if we ever launch one, mission planners will have to include some high-tech gym kit on the craft to maintain the muscles and bones of those on board.

Case study: Tim Peake 

Tim Peake, a British born astronaut, left the Earth’s atmosphere for the ISS in December 2015 and returned to European soil in June 2016. One of his biggest achievements while in orbit was joining in running the London Marathon, which he completed in just 3 hours and 35 minutes.

In order to do this, Tim had to train using a special treadmill, static bike and resistance-training machine for at least two hours every day, attaching himself to the equipment using a specially designed harness to combat weightlessness. This was on top of his marathon preparation at home, to make sure he didn’t lose his body conditioning while in space and end up in an unsafe condition to compete.

On returning to Earth, Tim had to have many different medical tests done to monitor his progress and help medical teams understand the physiological and psychological effects of returning from space. Despite originally complaining about “the world’s worst hangover” (dizziness and vertigo are common problems when readjusting to gravity) and having to learn how to walk again, weeks of strict rehabilitation diets and exercise plans have got Tim back on track, as you can read about on his blog. However, it could take him up to three years to regain the bone mass he lost while in space.

Tim Peake holds union flag behind him after returning from the ISS

During his time away, Tim worked on 250 different experiments and delivered lessons to over 40,000 students via video link as part of the Cosmic Classroom project. 


About this resource

This resource was first published in ‘Exercise, Energy and Movement’ in January 2012 and reviewed and updated in August 2016.

Ecology and environment, Physiology, Health, infection and disease
Exercise, Energy and Movement
Education levels:
14–16, 16–19, Continuing professional development