Black Bears Maintain Muscle Tone During Winter Slumber

Unlike humans, who lose muscle tone and strength if they don’t use their limbs for long periods of time, hibernating black bears do not, researchers at the University of Wyoming in Laramie report in today’s Nature. They can emerge from their winter slumber after three months without a morsel of food or a drop of water and maintain more than three-quarters of their original muscle strength. If people were immobile for the same period of time they would lose about 90%.

The researchers think the key to how black bears manage to preserve muscle tone is in the number and size of muscle cells and their protein content. In humans, muscle cells are reduced after periods of confinement or weightlessness, but muscle biopsies from black bears done at the start and finish of hibernation show they maintain their muscle cells. The scientists said the animals could be conserving muscle protein and strength by diverting protein from other places in the body and by stimulating their muscles by shivering.

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Compiled by Times medical writer Thomas H. Maugh II