How space travel reshapes the body: From muscles to mental health

In the absence of gravity, muscle mass disappears because the resistance training stops. When the astronaut returns to normal gravity, the heart may have weakened and may not function properly

The return of Sunita Williams and Barry “Butch” Wilmore from the International Space Station has sparked public interest in the health implications of spending long periods in space. The duo were up for 286 days instead of the eight originally scheduled.

 

Keeping people healthy in space is a complex task. Fifty years of research into this has resulted in major advances in our understanding of the body, and the development of many useful tools.

 

Running space stations, (or taking trips to Mars as Nasa plans) involve very long stints in space. It should be noted that Williams and Wilmore were nowhere near the record. Indeed, this wasn’t even the 10th-longest unbroken period in space. More than 20 astronauts and cosmonauts have spent over 300 days in space at one go, and quite a few have logged over 800 days spread across multiple missions.

 

The record for the longest single stay was set by Valeri Polyakov, who spent a whopping 438 days on the Mir Station in 1994-95. Polyakov died in 2022, at the ripe old age of 80, 27 years after returning to Earth and continuing to work in the aerospace industry.

 

Space travel places several unusual stresses on the body. One is due to acceleration, as a rocket gains speed. Acceleration pressures are often measured in “g”s  – that is, multiples of gravity. Gravity at sea-level exerts a downwards acceleration of around 9.8 metres per second every second (the velocity of a fall increases by 9.8 metres every second if you jump out of a plane). During sharp acceleration, fighter pilots can endure the equivalent of 9-11 times that of gravity. It requires special seats, pressure suits, and very high levels of fitness to ensure pilots don’t faint during such periods. Astronauts are usually pilots and they’re checked carefully to ensure they can handle high g-s.

 

The space station itself, or any vehicle the astronaut is travelling in, must be protected from radiation. The Earth has the useful combination of a thick atmosphere and radiation belts, thanks to its magnetism. The atmosphere and the radiation belts (these are called Van Allen Belts) block and capture highly charged particles emanating from the Sun.

 

Beyond these belts, there’s no barrier to harmful radiation, which can burn skin and cause cancer (instruments also need protection). Radiation shielding requires special materials. This may be the biggest problem in colonising Mars. The red planet doesn’t have much of a magnetic field or atmosphere, and deadly radiation irradiates its surface.

 

The vehicle must also have oxygen, and ways to handle poisonous and noxious waste products such as carbon dioxide (which we breathe out), urine and faeces. Space stations and lunar modules have systems to efficiently recycle wastes, re-extracting oxygen and water. Variants of the systems developed for such recycling are also used on Earth by municipalities to manage sewage disposal and capture atmospheric carbon.

 

While acceleration during a trip leads to high gravity, the space station itself, and any vehicle far enough from the Earth, has microgravity, or zero-gravity. This might sound like fun but it complicates everything – from writing, to eating and drinking. Many of the things we do depend on working with, or against, gravity. Water will not pour, a chicken leg will not stay on a plate, and a pen may not work without gravity. (Astronauts wear special diapers, and space toilets are designed for zero-gravity.)

 

Our muscles are also used to constantly fighting against 9.8 metres per second squared. In the absence of gravity, muscle mass disappears because the resistance training stops. Blood pressure and other physical systems can misbehave. 

 

When the astronaut returns to normal gravity, the heart (which is made of muscle) may have weakened and may not function properly.

 

Space vehicles are cramped and there may not be a doctor on the crew. A range of telemetering instruments – tools for checking blood pressure and mass (weight doesn’t exist but mass does), pulse rates, MRIs – were developed to enable remote monitoring of health parameters. 

 

Telemedicine essentially exists due to the needs of space travellers. And yes, a whole range of compact gym machines were also developed to help astronauts exercise and maintain fitness in zero-gravity. Most of the equipment you find in a well-equipped modern gym, and a lot of the equipment you find in a modern medical facility, were originally developed for space.

 

There’s a final frontier, which isn’t really talked about much: Keeping people sane during long periods of isolation. There was the famous case of the “astronaut love triangle”, when a jealous astronaut tried to kill a romantic rival (another astronaut), driving 900 miles to carry out the assault while wearing special diapers, so she wouldn’t have to take a toilet break. But that is probably a statistical aberration. 

 

Astronauts and cosmonauts are evaluated by psychiatrists before, during and after missions to try and ensure they are mentally stable. Hundreds of people have been in space without trying to kill each other, so the psychiatrists seem to have worked things out. Again, insights gleaned from those experiences have helped keep workers stable in other high-stress environments, like oil rigs and saturation diving vessels.