Why Bears Don't Lose Muscle Mass During Long Hibernation

Japanese scientists say they have observed "increased muscle mass" in cultured skeletal muscle cells

human, filled with bear serum. This confirms that something in the animals' blood is responsible for their ability to prevent muscle atrophy despite months of inactivity in hibernation.

Discuss

In winter, bears can lie in their dens 5-7months without food or drink. And people only need three weeks of inactivity to lose muscle mass. Bears survive hibernation with limited muscle loss and almost no damage.

By studying this phenomenon, the researchers found thata serum derived from the blood of black bears weakens the "destruction mechanism" that controls muscle degradation. The scientists attributed this to downregulated expression of the MuRF1 protein, a switch that triggers damage to unused muscles.

Scientists have also observed increased levelsinsulin-like growth factor 1 IGF-1 in the serum of a sleeping bear. The researchers hypothesized that higher concentrations of IGF-1 could be associated with a decrease in serum water content caused by dehydration.