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uni'wissen 02(4)-2011_ENG

Science at zero gravity: Researchers perform experiments on parabolic flights to determine whether nerves and muscles react the same way in a weightless environment as they do under the influence of gravity. Photo: Hoffmann/Multhaupt DLR Countdown. Full throttle. The pilots steer the airplane up into the sky, at a 45 degree an- gle. The gravity inside the plane is twice as strong as on the Earth’s surface. Even just lifting one’s foot off the floor is a chore. Then the rush of acceleration begins to subside. The gravita- tion diminishes, and the passengers begin to lose contact with the floor. “There is no up or down; it’s similar to being in water, only there isn’t any resistance at all,” says Ramona Ritzmann, doctoral candidate at the Institute of Sports Science and Physical Education of the University of Freiburg. The airplane continues to ascend for a brief moment and then starts to fall. After two and a half kilometers the turbines spring into life and pull the machine back up. In the blink of an eye, the gravity is as strong as it was during the ascent. The weightlessness last- ed a total of 22 seconds. The pilots bring the air- plane back into a horizontal position, thus com- pleting the parabola, and then immediately initiate a new one. They repeat the maneuver up to 30 times, giving scientists the chance to con- duct experiments in a zero-gravity environment: to grow crystals, to investigate the properties of materials – or, like Ramona Ritzmann, to test prototypes of exercise equipment designed to keep astronauts in shape during a journey into outer space. The crew of the International Space Station (ISS) is already required to exercise three hours a day, for instance with steppers or exercise bi- cycles. Even so, the astronauts cannot walk un- aided after returning to Earth. They lose an aver- age of ten percent of their muscle mass and one percent of their bone substance each month, particularly in the legs and the upper body, be- cause the muscles no longer exert enough pres- sure on the bones. “The bodily functions degen- erate because they are not placed under any strain in a weightless environment. It’s like an elderly person who lies in bed all day without moving,” explains Ritzmann. Astronauts also lose the ability to maintain a proper posture un- der the influence of the Earth’s gravity. However, the international space agencies are planning missions to Mars on which astronauts will be in space for three years at a time, says Prof. Dr. Al- bert Gollhofer, Director of the Institute of Sports Science and Physical Education: “The exercise methods currently in use are not sufficient for such a long journey.” Interplay between Nerves and Muscles Gollhofer is head of a Freiburg research team that is developing new approaches for exercise in weightless environments. The team includes ex- perts for bones, muscles, and the circulatory sys- tem, among other things. The scientists are inves- tigating the interplay between nerves and muscles. Every movement starts with a signal from the ner- vous system. These signals may be sent by the brain, as in the case of conscious movement, or they may be sent involuntarily by the sensors in the locomotor system. “We want to reach a more precise understanding of the source of move- ments and use this knowledge to improve exercise methods,” says Ritzmann. The sports scientist measures neuromuscular adjustment mecha- nisms in test subjects trying out new exercise ma- chines. “This allows us to determine how effective- ly the exercises activate the nerves and muscles.” However, the machines are only suitable for use in space if the body reacts to them in a weight- less state in the same way as it would under the influence of gravity. The purpose of the parabolic flights is to provide evidence of this. “The 22 sec- onds of weightlessness are sufficient to determine whether the muscles are controlled by the nervous system in the same way,” says Ritzmann. She has taken parabolic flights to try out the exercise ma- chines herself: “So far it seems as if the muscles exhibit comparable activities in a state of weight- “The bodily functions degenerate because they are not placed under any strain in a weightless environment” 21uni'wissen 04