Bears are perhaps the best-known hibernator species. Brown bears (Ursus arctos) hibernate to conserve energy during the winter where environmental conditions are harsh and food is scarce. Hibernation is characterized by physical inactivity and reductions in heart, breathing, and metabolic rates. In fact, bears can decrease their metabolic rate to ~25% of their basal rate during hibernation. Interestingly, they only experience a moderate drop in body temperature while hibernating, in contrast to other mammalian hibernators whose body temperatures can drop to near ambient temperatures.
A unique feature of hibernation is the lack of significant muscle wasting even during months-long periods of inactivity. For humans, months of physical inactivity would result in significant muscle loss, which can cause major metabolic and health issues, but bears remain inactive for up to 7 months a year without eating or drinking anything and without active arousal periods, yet they don’t display nearly as much muscle loss over this prolonged inactive period. Our lab is working to uncover how bears do this by analyzing various molecular mechanisms and biochemical processes to identify pathways that are uniquely expressed during hibernation. Understanding how hibernating mammals are able to withstand months of inactivity with minimal or no muscle atrophy or loss of strength could be used to help fight human muscle wasting and metabolic disorders as a result of ageing or physical inactivity.