THIS WEEK the heart adapts to low gravity, no longer having to work as hard to pump blood to the upper body. Returning to Earth put extra strain on the astronauts’ hearts: all had low haemoglobin levels and blood pressure, which made it difficult for them to stand up without fainting. Even more worrying were the effects of microgravity on bone and muscle, which are known to break down when not bearing the body’s weight. In an effort
“On their return to Earth, all the astronauts had trouble standing for any period of time”
Space trips make us weak at the knees Jo Marchant
FROM blackout-inducing g forces to withered muscles and bones, there aren’t many tougher physical challenges than going into space. This has been highlighted by the release of medical records from astronauts who worked on board the Russian space station Mir, which detail the gruelling effects space travel has on human health before, during and after a mission. Along with research on muscle wastage in astronauts on the 8 | NewScientist | 28 August 2010
International Space Station (ISS), the records demonstrate the need for better countermeasures against the hazards of living in space before any interplanetary missions are attempted. The records were collected by Gilles Clément of the International Space University in Toulouse, France, and colleagues, who oversaw the selection, flights and rehabilitation of six European astronauts who worked on board Mir between 1988 and 1999. They have only just been
to combat this, the astronauts exercised on treadmills and bikes, but they still lost up to 2 per cent of their bone mass each month (Advances in Space Research, DOI: 10.1016/j.asr.2010.05.023). Such problems would pose a serious hazard to astronauts travelling to other planets. It would take around nine months to travel to Mars, for example, and once in the Martian gravity astronauts would be too weak to work, and susceptible to blackouts and broken bones. –Good for memories, bad for health– Several studies of astronauts who worked on the ISS have released because the astronauts confirmed the problem of muscle requested a 10-year delay. wastage. Bob Fitts of Marquette Prior to take-off, the researchers University in Milwaukee, used stringent tests to rule out Wisconsin, and colleagues took anyone susceptible to health calf-muscle biopsies from nine problems (see “So you want to astronauts and cosmonauts be an astronaut?”). Even so, three before and after six-month-long of the astronauts experienced missions on the ISS. On their motion sickness. Overall, however, return, the crew were visibly frail. the screening was successful: “They all had trouble standing for during seven missions lasting any period of time,” says Fitts. between 14 and 189 days, there Although the ISS astronauts were only a handful of minor had done resistance training and health problems, such as headache, aerobic exercise while in orbit, insomnia and congestion, all they still experienced muscle treatable with drugs kept on board. wastage. On average, their calf The real problems began muscles generated 30 per cent less when the astronauts returned power. There was also a switch home. Their bodies had adapted from slow-twitch muscle fibres, to weightless conditions, so which normally bear the constant returning to Earth was a shock to weight of the skeleton, to fastthe system. For example, in space, twitch fibres, responsible for
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shorter bursts of movement. Fitts measured a 35 per cent decrease in the force of the slow fibres and a 40 per cent drop in power – equivalent to having the muscles of an 80-year-old (Journal of Physiology, DOI: 10.1113/ jphysiol.2010.188508). So how can humans survive a trip to another planet? Suggestions range from using a giant centrifuge to simulate gravity to developing a pill that would block bone and muscle loss. However, keeping space travellers in shape may just be a matter of improving their exercise regimes. Short bursts of high-intensity resistance training, at around 70 per cent of the muscles’ maximum capacity for 15 minutes, twice a day, should help, says Fitts. A range of studies in animals and volunteers confined to bed rest suggest this will protect muscles better than long periods of low-intensity aerobic exercise. It may also guard against bone loss. Dan Bikle of the University of California, San Francisco, who has studied bone loss in rats whose hindquarters are suspended off the ground, recommends intense weightbearing exercise for 1 second in 10, for a few minutes each day. The problem is that in space, weights are, of course, weightless. The astronauts on the ISS pulled against bungee cords but complained it was “like lifting
So you want to be an astronaut? Budding astronauts beware: getting to the launch pad can be as tough as the mission itself. The European astronauts who worked on the Russian space station Mir between 1988 and 1999 were selected using screening processes organised by the French and European space agencies. The tests saw 1065 candidates from across Europe whittled down to just 13. Most fell at the first hurdle – a check of academic and professional qualifications, plus a wide-ranging medical questionnaire. Candidates were then subjected to extensive medical and psychiatric examinations. They needed to have flawless vision and hearing, and to be the right size to fit inside the cramped Soyuz vehicle that would ferry them to Mir.
barbells with no weights attached”. NASA is now testing a device that uses vacuum cylinders to provide greater resistance. For the biggest benefits, astronauts must start their exercise regime as soon as they get into space. In work that is yet to be published, Ken Baldwin of the University of California, Irvine, found that once rats’ muscles stop bearing body weight, the genes that code for the proteins myosin and actin – key components of muscle – shut down within 12 hours. Once this degeneration starts, it is hard to reverse. This is bad news for astronauts, who tend to be busy with mission tasks when they first arrive, or feel too sick to train. “They take too long to get into their training mode,” says Baldwin. Finally, space travellers must eat all the food assigned to them. Astronauts tend to lose their appetites, which contributes to their loss of fitness: if you don’t eat enough calories you can’t build muscle. High-protein meals immediately after training should keep their muscles ticking over until they feel the pull of –Experimenting on Mir– an alien planet. n
The remaining 272 candidates were subjected to a battery of physiological tests. To rule out anyone susceptible to motion sickness, candidates had to tilt their heads and torsos while being spun around at 30 revolutions per minute. Anyone experiencing severe symptoms was out of the running. Next, the would-be astronauts were placed in a centrifuge and subjected to eight times the force of gravity for 30 seconds. Anyone who lost consciousness or suffered an irregular heartbeat failed. Then there was the tilt test, in which subjects were held at various angles to the ground. A dangerous drop in blood pressure and you were out. Candidates also had to sit in an altitude chamber at the equivalent of 10,000 metres, and were brought to sea level in just 30 seconds. Again, any
who lost consciousness were cut. They also had to demonstrate minimum fitness requirements for their age. For example, a 40-year-old had to run a kilometre cross-country in 4 minutes 10 seconds, and to sprint 100 metres in 16.8 seconds. All this was topped off with an interview with space agency management, before the final selection was made. Exhausted yet? The would-be astronauts then had to complete a basic training programme, before travelling to Russia’s training facility in Star City near Moscow for mission-specific training. There they were subjected to monthly medical tests, before being placed in quarantine for the final two to three weeks before flight to avoid picking up any last-minute infections. Finally, they were ready for take-off.
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