One of the main problems that astronauts face on long space journeys is the loss of muscle tissue, due to long periods without enough exercise. Bears solved this problem long ago-they lose hardly any muscle when they hibernate.

Henry Harlow of the University of Colorado wanted to find out why. He believes that bears have evolved a way of conserving muscle tissue so that if they are disturbed by predators, such as wolves or mountain lions, they will still be able to get away.

He and his team have been analyzing muscle samples from black bears in the Rockies. They’ve found that the bears lose only 22 percent of their muscle strength over a long winter’s sleep.

“They don’t eat, drink or pee for 130 days,” he says. “The bear reabsorbs urea through the bladder and uses the nitrogen to conserve protein.” It’s a shame that won’t work for astronauts, since it would also solve another major problem of long space flights, but if humans tried the same thing, they would suffer from a severe poisoning called uremia.

The scientists placed thermometers on sleeping bears and found that their core body temperatures remained constant, while temperatures in their neck regions spiked around 4 times a day. This indicated that the bears “exercise” by shivering periodically while they sleep. Astronauts may be able to learn to do the same thing.

Harlow and his team have put transmitting collars on the bears they study. They creep into the caves where the bears are hibernating, armed only with a flashlight and a syringe containing a sedative. “None of my crew have been damaged by a bear, and we’ve probably been in around 300 bear dens,” he says.

Once they give the bear a shot of the sedative, it falls asleep in 15 minutes and they haul it outside on a blanket to do their tests. They take a tissue biopsy the size of a pea, then return the bear to its cave. It wakes up in the spring with a few bad dreams, but no traumatic memories.

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