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Why do weightless bodies have to vibrate?

“It is a totally new feeling,” said Ramona Ritzmann from the University of Freiburg referring to the feeling of weightlessness she experienced during her experiments on board the Airbus 300. Something that can trigger amazing sensations over a short period of time, can have seriously negative consequences for astronauts. Prolonged stays aboard the International Space Station ISS can lead to muscle degeneration. Along with her colleagues Andreas Kramer and Prof. Dr. Albert Gollhofer from the Institute for Sports and Sports Science at the University of Freiburg, Ritzmann is investigating whether these effects can be counterbalanced by training. Their research is part of the Zero-G project and is aimed at developing training programmes for a future generation of astronauts. The Freiburg scientists have come up with ideas for a training programme requiring only minimal effort by the astronauts.

The Zero-G Airbus 300 used to simulate weightlessness during an elliptic flight path relative to the centre of the Earth. © Wikipedia

The "parabolic" flight path gives those aboard around 22 seconds of weightlessness, achieved by "freefall" through the air during which gravity is the only force that acts on the aircraft and its contents. This effect lasts until the aircraft has completed approximately half of its upward trajectory.

The aircraft, which is equipped with a broad range of scientific devices, has both scientists and volunteers on board. The volunteers are an important factor in the researchers' investigations and help Ramona Ritzmann and Andreas Kramer from the Institute for Sports and Sports Science to examine how the nervous system and the muscles react to weightlessness, information that they will use in their doctoral theses. It has been known for many decades that the lack of stress on the body during weightlessness has severe consequences. After about two months in space, astronauts generally lose around thirty per cent of their muscle mass. "As the muscles are no longer able to exert enough strength on the bones, the latter will also lose substance" said Prof. Dr. Albert Gollhofer, head of sports motorics at the ISS and project supervisor. "The bone mineral density can decrease by up to four per cent in two months," said Kramer. "It takes more than a year for the bone structure to fully regenerate." 

Counteracting the lack of gravity

Training whilst resting: During whole body vibration, a volunteer lies on his/her back and a disc at his/her legs generates high-frequency contractions in the volunteer’s body. © University of Freiburg

Aerospace institutions such as NASA or ESA are extremely interested in investigating training measures that could help their astronauts protect themselves against the effects of weightlessness. Whole body vibration is one such training measure. As part of Zero-G, a cooperative project between the ESA, the German Aerospace Centre (DLR), the Pforzheim-based manufacturer Novotec medical  and the University of Freiburg, Gollhofer, Ritzmann and Kramer are investigating the effects of training during weightlessness. They are particularly interested in how muscular activity changes at zero-G with or without training using the new method. "We want to find out how the neuromuscular system behaves when mechanical stimuli are absent," said Gollhofer. Ramona Ritzmann has developed a study involving the recording of electrophysiological parameters using electromyograms (EMG). "Fourteen volunteers are taking part in the study," said Ritzmann explaining that the researchers have participated in seven parabolic flights since September 2009, during which they examined the effect of whole body vibrations on the volunteers.

Inside an Airbus 300 during the experiments: in order to investigate the behaviour of muscles during whole body vibrations, electrophysiological measurements are carried out on the lower leg muscles. © University of Freiburg

Is this kind of training really able to counteract muscle and bone wastage during weightlessness? This question is bound to arise when the training programme appears to consist of doing nothing but lying on one's back. The volunteers lie in the training device where they are pushed via straps securing their legs against a disc that emits high frequency vibrations. The force that acts on the disc via the straps corresponds to the volunteer's normal weight on earth. The trick behind whole-body stimulation is that the muscles need to constantly withstand the impact exerted by the disc at a frequency of 25 Hz. This causes the muscles to contract 25 times per second. The effect spreads from the legs to the rest of the body. The muscles virtually train on their own. Such ‘bed-rest' studies have already been used for earthbound experiments  where volunteers have to spend several weeks in bed without moving. Such experiments showed that the inactive muscles wasted in the control group, but not in the volunteers who were subjected to the vibrations.

Is this an easier alternative?

It is still too early to make definite statements on the effect of such whole-body vibrations. “Nevertheless, preliminary results appear to be very promising,” said Ritzmann. This suggests that whole-body vibrations might be an excellent training tool in space. “How does this training actually work?” asks Gollhofer. “Do whole-body vibrations have a particular effect on the neuromuscular system? What happens during vibration?” The researchers still have to find answers to these questions. If the training is really as effective as it appears to be, it could very well be tested in space in the not too distant future. NASA and ESA are particularly interested in lightweight devices that can be cheaply transported into orbit. “Transporting a device of this kind to ISS costs several million euros,” said Kramer. At present, astronauts use treadmills for training whose bulk and weight make them even more expensive to transport. And on top of the expense the astronauts have to expend energy to run on the treadmills, whilst training in a prone position appears somewhat more appealing!

Further information:
Ramona Ritzmann
Scientific Officer (Motorics)
Institute for Sports Sports Sciences
University of Freiburg
Schwarzwaldstraße 175
D-79117 Freiburg i. Br.
Tel.: +49 (0)761/203-4557
Fax: +49 (0)761/203-4534
E-mail: ramona.ritzmann(at)sport.uni-freiburg.de
Website address: https://www.gesundheitsindustrie-bw.de/en/article/news/why-do-weightless-bodies-have-to-vibrate