Japanese researchers recently observed "muscle gain" in cultured human skeletal muscle cells infused with serum from hibernating black bears, verifying that distinctive factors stimulated in the blood in winter initiate their exceptional ability to stop muscular atrophy despite months of lack of activity.

However, as specified in a EurekAlert! report, what these key blood components stay unknown. Essentially, hibernating bears can lie still for five to seven months each year inside their dens, minus eating or drinking. In humans, only three weeks of no activity is enough to lose muscle mass.

 

Prolonging it could result in sedentary lifestyle-associated illnesses such as diabetes and obesity, and even death.

Bears, nonetheless, can survive their hibernation with limited muscle loss, minimal metabolic dysfunction, and unharmed physical functions.

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Bear
(Photo: Pexels/Brett Sayles)
Hibernating bears can lie still for five to seven months each year inside their dens, minus eating or drinking.


'Use-It-or-Lose-It Phenomenon'

The so-called "use-it-or-lose-it phenomenon" is a well-accepted physiological principle for the skeletal muscle, mostly plastic, in reaction to functional demands.

According to associate professor Mitsunori Miyazaki from Hiroshima University's Graduate School of Biomedical and Health Sciences, inactivity usually results in loss of skeletal muscle and metabolic dysfunction in many animal species, including humans.

On the contrary, hibernating animals are likely better described to be under the phenomenon known as "no use, but no lose," in that there is possible resistance to muscle atrophy during continuous inactivity conditions.

The joint research with researchers from Hokkaido University discovered that the serum drawn from hibernating Japanese black bears' blood "weakened the destruction mechanism, controlling degradation of muscles. Their findings were published in the PLOS ONE journal.

IGF-1 in Hibernating Bears

The researchers observed, too, levels of the growth factor hormone called insulin-like growth factor-1 or IGF-1 in the hibernating bear serum.

They identified it as a candidate upstream factor that induces the Akt/FOXO2a axis stimulation.

Past studies have reported seasonal divergences of IGF-1 concentrations in bear serum. Such studies showed that the said concentrations were highest during the active summer season and lowest during early hibernation and then rose again close to the end of hibernation.

However, Miyazaki and his team later redirected their attention elsewhere following the correction of their calculation on IGF-1 concentration levels in the serum of the hibernating bears.

Controlling Protein Metabolism

The team said it is a probability that the higher IGF-1 concentrations observed in the research were simply due to a drop in the water content of the serum brought about by other causes like dehydration, among others.

Miyazaki explained they have specified that some factors present in hibernating bear serum may control protein metabolism in cultured human skeletal muscle cells and add to the maintenance of muscle mass. Nonetheless, the identification of this facto has not yet been attained.

The associate professor, originally a physical therapist, said he wondered why it is not plausible to develop muscles that do not weaken in the first place instead of restoring deteriorated muscles.

The professor added, that he wanted to conduct a study that would lead to developing rehabilitation and training approaches. He also said that this is the reason he got interested in exploring the secrets of hibernation.

By determining this factor in hibernating bear serum and clarifying the unexplored mechanism behind muscles that are not weakening even without use in hibernating creatures, it is plausible to develop effective tactics in humans and avoid turning bedridden in the future.

Related information about hibernating bears is shown on Conrad Jensen's YouTube video below:

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