Hibernating Bears Conserve Muscle Strength and Maintain Fatigue Resistance

  title={Hibernating Bears Conserve Muscle Strength and Maintain Fatigue Resistance},
  author={Thomas Lohuis and Henry J. Harlow and Thomas D. I. Beck and Paul Anthony Iaizzo},
  journal={Physiological and Biochemical Zoology},
  pages={257 - 269}
Black bears spend several months each winter confined to a small space within their den without food or water. In nonhibernating mammals, these conditions typically result in severe muscle atrophy, causing a loss of strength and endurance. However, an initial study indicated that bears appeared to conserve strength while denning. We conducted an in vivo, nonsubjective measurement of strength, resistance to fatigue, and contractile properties on the tibialis anterior muscle of six hibernating… 

Soleus muscle stability in wild hibernating black bears.

The ability of the black bear to preserve the biochemical and performance characteristics of the soleus muscle during prolonged hibernation validates the ability of this mammal to resist skeletal muscle atrophy during hibernation.

Hibernating black bears (Ursus americanus) experience skeletal muscle protein balance during winter anorexia.

  • T. LohuisH. HarlowT. Beck
  • Environmental Science
    Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology
  • 2007

Skeletal muscles of hibernating brown bears are unusually resistant to effects of denervation

Hibernating bears alter skeletal muscle catabolic pathways regulated by neural activity, and exploration of these pathways may offer potential solutions for disuse atrophy of muscles.

Avoidance of Skeletal Muscle Atrophy in Spontaneous and Facultative Hibernators

It appears that regardless of the phenotypic expressions of hibernation, the outcome is the conservation of skeletal muscle in the winter season of reduced activity and food intake.

Muscle Protein and Strength Retention by Bears During Winter Fasting and Starvation

Black bears during 150 days of inactivity and complete food deprivation show no cardiac left ventricular atrophy and skeletal muscle exhibits no or only marginal loss of protein, fiber number, size, or conversion of slow oxidative to fast glycolytic fiber composition with a concomitant retention of strength.

Skeletal muscle mass and composition during mammalian hibernation

Despite massive reductions in activity and nutrient intake during winter, hibernators largely preserve skeletal muscle, enabling hibernating animals to resume active behaviors immediately following terminal arousal in the spring.

Minimal Seasonal Alterations in the Skeletal Muscle of Captive Brown Bears

The results agreed with a study that showed minimal skeletal muscle atrophy between seasons in wild black bears, and the half‐rise time in the twitch contractions increased in winter relative to summer samples, which is unexpected under disuse conditions.

Muscle plasticity of Inuit sled dogs in Greenland

Skeletal muscle of Inuit dogs responds flexibly to changes in functional demands: mitochondrial numbers, lipid droplet size, and the number of contractile filaments all increase with increasing workload and food supply while the capillary network remains unchanged.

Lowering metabolic rate mitigates muscle atrophy in western fence lizards

It is suggested that metabolic rate alone can influence the rate of Muscle atrophy and that ectothermic vertebrates may have an intrinsic mechanism to resist muscle atrophy during seasonal periods of inactivity.

Comparative functional genomics of adaptation to muscular disuse in hibernating mammals

A large‐scale gene expression screen in hind limb muscles comparing hibernating and summer‐active black bears and arctic ground squirrels using custom 9600 probe cDNA microarrays showed an elevated proportion of overexpressed genes involved in all stages of protein biosynthesis and ribosome biogenesis in muscle of both species during torpor of hibernation, suggesting induction of translation at different hibernation states.



Protein Use and Muscle‐Fiber Changes in Free‐Ranging, Hibernating Black Bears

The findings suggest that hibernating bears, particulary female black bears, use only fatty tissues as a metabolic substate during hibemation.


It is suggested that bears engage in bouts of muscle activity during the winter denning period that may result in the retention of muscle strength without elevating their core body temperature and without arousing from torpor.

Disuse atrophy in the hibernating golden-mantled ground squirrel, Spermophilus lateralis.

Disuse (inactivity, bed rest, and spaceflight) may lead to a loss of muscle mass and a decrease in oxidative capacity in skeletal muscle, but in contrast to many other disuse studies, oxidative capacity was increased significantly in the gastrocnemius and semitendinosus.

Maintaining muscle mass during extended disuse: aestivating frogs as a model species.

The role of reactive oxygen species and antioxidants during muscle disuse is emphasised, and the metabolic depression that occurs during dormancy would appear to have a protective role, reducing or preventing muscle atrophy despite periods of inactivity lasting 6-9 months.

Functional and structural adaptations of skeletal muscle to microgravity.

The major effects of space travel on skeletal muscle with particular emphasis on factors that alter function are muscle atrophy and the associated decline in peak force and power, and weightlessness reduces the ability of the slow soleus to oxidize fats and increases the utilization of muscle glycogen, at least in rats.


It was showed that pregnant females in a state of diapause during early winter had about 89% larger fat depots than did nonreproductive females going into hibernation, and rates of overall protein loss were relatively small.

Characteristics of diaphragm muscle fibre types in hibernating squirrels.

Morphometric and metabolic indices of disuse in muscles of hibernating ground squirrels.

Gluconeogenesis in arctic ground squirrels between periods of hibernation.

This study follows a number of metabolities in tissues and body fluids to assess the sources for reconstitution of the glucose reserves: lactate, urea, ammonia, free fatty acid, glycerol, triglyceride, and glucose in plasma; glycogen in liver and muscle; and urea and ammonia nitrogen in urine.