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HIROSHIMA, Japan — All it takes is a few weeks of lounging and putting off the gym for humans to start losing muscle mass, but bears sleep all winter long and wake up looking just as buff. Now, exciting new research out of Japan has found that the “superhero” properties in bear blood can also help humans gain muscle too!

Scientists at Hiroshima University observed “muscle gain” in cultured human skeletal muscle cells infused with serum from hibernating black bears. They say their work confirms that “unique factors” activate in a bear’s blood during winter, sparking their incredible ability to retain their muscles and prevent muscular atrophy despite remaining stationary for five to seven months at a time. However, exactly what these key blood components are is still a mystery.

“The ‘use it or lose it’ phenomenon is a well-accepted physiological principle for the skeletal muscle, which is highly plastic in response to functional demands. Disuse typically leads to skeletal muscle loss and metabolic dysfunction in many animal species, including humans,” explains first study Mitsunori Miyazaki, associate professor at Hiroshima’s Graduate School of Biomedical and Health Sciences, in a university release.

“In contrast, hibernating animals are likely better described to be under the ‘no use, but no lose’ phenomenon, in that there is potential resistance to muscle atrophy during continued disuse conditions.”

In collaboration with researchers from Hokkaido University, study authors discovered that serum extracted from the blood of hibernating Japanese black bears actively weakens the “destruction mechanism” that dictates muscular degradation.

Here’s why hibernation blood is special

A living being’s muscle mass is generally influenced by the dynamic balance between the “synthesis” and “degradation” of its proteins. When a bear’s serum interrupts this balance, cultured muscle cells display significant protein growth after just 24 hours of treatment. Importantly, serum taken from bears during the summer months did not have this same effect on muscle cells.

Researchers theorize the diminished capacity of the muscles’ “destruction mechanism” is due to the suppression of the MuRF1 gene (Muscle RING-finger protein-1), which scientists consider the switch that jumpstarts the shredding of unused muscles. According to the theory, the activation of the Akt/FOXO3a (protein kinase B/Forkhead box class O 3a) axis takes care of the elevation of protein synthesis — mediating the suppression of MuRF1 expression.

The team also found higher levels of the growth factor hormone IGF-1 (insulin-like growth factor-1) in the hibernating bear serum. Study authors say this hormone is a potential upstream factor, inducing the activation of the Akt/FOXO3a axis. Meanwhile, earlier studies have recorded IGF-1 concentration variations in bear serum depending on the season. Those earlier projects noted that IGF-1 concentrations were highest during the active summer months and at their lowest during the early weeks of hibernation (before increasing again near the end of the winter).

Could this lead to a treatment for bedridden patients?

Prof. Miyazaki and his team redirected their efforts elsewhere after properly correcting their calculations regarding GF-1 concentration levels within the hibernating bear serum. They believe that it is quite possible that the higher IGF-1 concentrations in the study are the result of a reduction in the serum’s water content — due to any number of other causes, including dehydration.

“We have indicated that ‘some factor’ present in hibernating bear serum may regulate protein metabolism in cultured human skeletal muscle cells and contribute to the maintenance of muscle mass. However, the identification of this ‘factor’ has not yet been achieved,” Prof. Miyazaki adds.

“I wanted to do research that would lead to the development of effective rehabilitation and training methods,” Prof. Miyazaki concludes, adding that this is the reason he started exploring hibernation’s secrets.

“By identifying this ‘factor’ in hibernating bear serum and clarifying the unexplored mechanism behind ‘muscles that do not weaken even without use’ in hibernating animals, it is possible to develop effective rehabilitation strategies in humans and prevent becoming bedridden in the future.”

The study is published in PLOS ONE.

About John Anderer

Born blue in the face, John has been writing professionally for over a decade and covering the latest scientific research for StudyFinds since 2019. His work has been featured by Business Insider, Eat This Not That!, MSN, Ladders, and Yahoo!

Studies and abstracts can be confusing and awkwardly worded. He prides himself on making such content easy to read, understand, and apply to one’s everyday life.

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