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Lessons
in Muscle Fitness
from Hibernating Bears
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.''
SOURCE:
Nature 2001;409:907.
Reference
Source 89
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