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Brief Communications

Nature 409, 997 (22 February 2001) | doi:10.1038/35059165

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Muscle strength in overwintering bears

Henry J. Harlow1, Tom Lohuis1, Thomas D. I. Beck2 & Paul A. Iaizzo3

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Unlike humans, bears retain their muscle tone when moribund for long periods.

Black bears (Ursus americanus) stay inside their winter den for five to seven months of the year, during which time their body temperature drops to about 4 °C below normal1 and they do not eat, drink, urinate, defecate or show any other perceptible activity2. Although inactivity in humans, for example as a result of confined bed rest, weightlessness or limb immobilization, leads to atrophy of skeletal muscle, loss of muscle tone and impaired strength, we show here that the black bear does not suffer a similar deterioration.