Lessons in Muscle Fitness From Hibernating Bears

By Alan Mozes

NEW YORK (Reuters Health) - Bears and bedtime conjure up cozy images of cuddling and nursery rhymes. But for those confined to bed following illness or injury, real-life hibernating ``Teddies'' could provide clues as to how to prevent muscle loss due to prolonged immobility.

``We found that bears lose about 22% of their muscle strength while hibernating for about 130 days, and humans that are bedridden lose over 80% during a comparable period--so these guys are doing something which is unique and unusual,'' said Dr. Henry Harlow, a professor in the Department of Zoology and Physiology at the University of Wyoming in Laramie, Wyoming.

Harlow and colleagues analyzed the effect on muscles of the annual 5- to 7-month winter hibernation of black bears. The findings are published in the February 22nd issue of Nature.

By determining body fat content and examining muscle tissue samples, the research team found that hibernating black bears--unlike humans in a comparable situation--do not suffer muscle fiber loss either in terms of number of muscle cells or size. Instead, the investigators determined that the bears maintain their ability to move quickly, if necessary, throughout the half year period--seemingly retaining their ``fight or flight'' capacity in spite of prolonged starvation and inactivity.

Harlow's team concluded that although the bears may appear to be immobile during hibernation--with a steep drop in body temperature and a total absence of eating, drinking, urination and defecation--they are, in fact, engaging in a range of activities designed to conserve energy and muscle.

The team noted, as an example, that upon close inspection the bears can be seen to be vigorously and rhythmically shivering throughout hibernation--stimulating muscles by what amounts to isometric contractions, a process similar to the clenching of a fist.

Harlow and colleagues also found that protein levels remained normal in many of the bears' muscles throughout hibernation. They theorize that the large animals keep their muscle tone up to scratch by recycling the urea nitrogen in retained urine back into usable protein.

The researchers concluded that both these processes could eventually provide insight into how to help patients who are subject to muscle disorders or protracted bed rest. The findings might someday even be of help to astronauts, who can lose muscle mass in the low-gravity environment of space.

Harlow told Reuters Health that the black bears may ultimately provide a new spin on the age-old adage ``use it or lose it''.

``The bears are doing things with medical implications,'' he said. ``If we can inoculate our own gut with the right kind of bacteria we could recycle urea much better...if we can simulate a kind of nerve-firing to specific muscle areas and do it in such a pattern that you keep muscles active even when a person is laying in bed, this may prove helpful.''