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Weightlessness and its effects on the human organism

The human body goes through a multitude of physiological changes in space

Shortly after leaving Earth’s atmosphere, the absence of gravity causes the astronaut’s height to increase by two or three centimetres. This is due to stretching of the vertebral column, which is no longer being pressed together by the downward pull of gravity. For the same reason, blood and other fluids migrate from the legs to the upper part of the body. The face swells, like it does after a prolonged headstand in the gym, and the veins of the neck protrude. Most astronauts initially feel disoriented because their senses are no longer able to tell them what is ‘up’ and what is ‘down’ – a distinction that has no relevance in space. This condition, known as space motion sickness or space adaption syndrome, can last for several days in susceptible individuals.

Many of these symptoms will have almost completely disappeared by the end of the first week, as the whole body adapts to the new conditions in space. Unfortunately, this process of adaptation also means that the body starts to break down everything it doesn’t need in a weightless environment, including our tough, heavy bones, which all of a sudden have no weight to carry.

As a result of all these physiological changes, it always takes a while for astronauts to readapt their bodies and their senses to the pull of gravity after their return to Earth. Many returning astronauts find it hard to keep their balance at first. Scientists conjecture that one of the reasons for this odd behaviour is the severe reduction in blood volume resulting from the redistribution of body fluids during adaptation to the weightless environment.

Medical and physiological aspects of weightlessness 

Today we have the evidence to prove that human beings can live in a weightless environment for long periods without any serious risk to their health. The major issue is not the time spent in space but the return to Earth, because astronauts’ health can be compromised if rehabilitation measures are not taken in time – mainly in the form of targeted physical exercise.

The following effects have been observed after a prolonged stay in weightless conditions:

  • Eyes: Angle of view drops from 10° to 15°.
  • Face: Blood and other fluids are redistributed to the upper part of the body, causing the face to look puffy or swollen.
  • Vertebral column: Stretches by several millimetres.
  • Heart: The left ventricle shrinks by up to 10%. This can result in greater fatigue.
  • Liver: The liver breaks down medication differently than on Earth. Doses have to be adapted accordingly.
  • Muscles: Because they are being used less and blood flow is reduced, muscles begin to waste away. A targeted exercise programme is necessary to reverse these effects.
  • Bones: Bones become softer due to mineral loss. Large quantities of calcium, in particular, are lost.
  • Legs: Blood and other fluids are diverted away from the lower part of the body. The legs become thinner, and the layer of hard skin on the soles of the feet disappears.
  • Blood: The number of red blood corpuscles falls. Diminished oxygenation can lead to reduced physical capacity.

Sport in spaceTo minimise the effects of the environmental conditions in space on the human skeletal and muscular system, astronauts are required to carry out a strictly timetabled programme of daily activities. Regular exercise forms an important part of every space mission. It helps the astronauts to prevent deterioration of their body functions and maintain the strength of muscles and bones. One hour of vigorous exercise every day is the prescribed minimum requirement.



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