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27/6/2016

The ups and downs of readapting to life on Earth

The ups and downs of readapting to life on Earth

Following Tim’s re-entry to Earth on 18th June, Blue Abyss’ Space Life Scientist, Professor Simon Evetts, tells us what Tim can expect over the coming weeks and months as he readapts to gravity.

Studying astronauts helps us to understand why and how the body deals with low or zero gravity. With each mission, we get closer to working out the optimum exercise to keep astronauts “Earth-strong”, and Tim’s return offers us an opportunity to advance this knowledge. There’s no doubt about it, the rigours of spaceflight leave a lasting effect on the body. Tim’s body will need to readjust to Earth’s gravity, and it can take anything between six weeks to three years for some aspects of the body to return to pre-flight normality after 6 months in Space. Getting used to the Earth’s gravity again is known as ‘readaptation’.

Let’s look at the challenges Tim might face in readapting, some of which might have short-term effects and some much longer.

In the first few days

The vestibular system of the inner ear controls balance and orientation, and is very sensitive to gravitational changes. In the weightlessness of Space, the vestibular system gets used to not working as designed, and on re-entry to Earth, the brain must relearn normal orientation associated with gravity. It’s really quite simply the difference between up and down. As the brain adjusts, this can result in dizziness, nausea and even vomiting. Luckily, Entry Motion Sickness as it is known, doesn’t last long.

One of the conditions that around 70 to 80% of astronauts also suffer from in the first day or two of their return is fainting due to low blood pressure. It’s a condition called Orthostatic Intolerance. In Space, blood volume decreases and a number of changes effect blood pressure control. This can cause blood pressure to drop too far, too fast when standing up. It only lasts for a day or so, but to help counter-act this, during re-entry astronauts wear anti-gravity garments around their legs and pelvis to reduce the blood pooling in the lower body.

You're excited to be back, but you can't fully enjoy the experience because, to be quite frank, you feel pretty terrible. It can only be described as something akin to the world's worst hangover in terms of everything that is going on in your head."

Tim told reporters at the European Space Agency’s press conference.

In the first 6 weeks

During his 6 months in Space, Tim will probably have experienced muscle loss and reduced cardiovascular fitness, even with his strict in-flight counter-measure training programme. Muscles, bones and connective tissues require force to be transmitted through them to retain their size and strength. Despite training for around 2 hours a day, muscles don’t work nearly as much as they do on Earth and rarely experience impact in the weightless environment. In fact, some astronauts find that they've suffered a 10 to 20% loss of muscle strength in the legs on their return to Earth.

Up to a year

If in-flight exercises are not fully effective, astronauts can lose up to 1.5% of their bone mass for each month spent in Space. It's also apparent that astronauts suffer from deconditioned stabilizer muscles around the spine. This increases the risk of back injury within the first few months of return and astronauts are generally at far greater risk of issues such as slipped discs in the first year of their return, than the general population. Bones do become weaker in Space, but the more impact exercise Tim does now and the better he eats, the less this effect is likely to be felt.

Longer term

In microgravity, changes in fluid pressures in the upper body resulting in increased pressure on the optic nerve have been linked to alterations in vision on return to Earth. A study by NASA found that near and distance vision became worse for 48% of astronauts after short-duration missions. Called Visual Impairment Syndrome, Tim may find that his vision is blurred for a while but this should eventually get better. Some astronauts, however, are left with permanent blurred and/or loss of peripheral vision. This is a Space medicine topic that the Space industry is trying to better understand.

What’s next for Tim?

Tim will spend at least three weeks recovering from the rigours of microgravity at the European Space Agency’s astronaut centre in Cologne, Germany. He’ll undergo a number of medical tests and intensive rehabilitation for several hours a day. This will start with getting his body used to gravity through physiotherapy and simple body weight exercises. He’ll work up to using physio-bands and pool aerobics, and build to more traditional exercise. His core in particular will need work, so he'll carry out exercises to target the inner muscles around his spine to help him readapt to gravity.

What’s amazing is how quickly the human body adapts to a new environment. I had the same experience when I went up into space and was amazed after just 24 hours, living on board the space station how quickly I was able to function. It’s a bit slower coming the other way, I can tell you, and it’s a bit harder,” continues Tim.

Tim is unlikely to experience any long-term effects from his time in orbit. It is possible that one or two of his bones might take a year or so to regain full mineral density, but Tim exercised a great deal, so I imagine that he's in good shape.

I, and the team at Blue Abyss, are glad that he’s safely home and wish him all the very best with his recovery.

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