Black Bears in the Wild Retain Muscle Strength During Hibernation

Abstract

Back bears hibernating through the winter at near normal body temperatures (34°C) have limited muscle disuse atrophy. Bears in their natural dens were fitted with a foot torque plate assembly to measure ankle dorsiflexion in response to supramaximal stimulation. Bears lost only 22% of their strength over a 130 day denning period which compares to a predicted 90% strength loss over the same period by humans either confined to bed rest or in a weightless environment. Additionally, six out of 8 muscle twitch parameters altered by muscle atrophy were unchanged by prolonged confinement. Understanding strength retention over an extended period of inactivity by bears has far reaching implications for human medicine and space travel.