The winter months are challenging for many animal species, which often enter a state of dormancy or hypometabolism to "wait out" the cold weather, food scarcity, reduced daylight, and restricted mobility that can characterize the season. To survive, many species use metabolic rate depression (MRD) to suppress nonessential metabolic processes, conserving energy and limiting tissue
atrophy particularly of skeletal and cardiac muscles. Mammalian hibernation is the best recognized example of winter MRD, but some turtle species spend the winter unable to breathe air and use MRD to survive with little or no
oxygen (
hypoxia/
anoxia), and various frogs endure the freezing of about two-thirds of their total body water as extracellular
ice. These winter survival strategies are highly effective, but create physiological and metabolic challenges that require specific biochemical adaptive strategies. Gene-related processes as well as epigenetic processes can lower the risk of
atrophy during prolonged inactivity and limited nutrient stores, and
DNA modifications,
mRNA storage, and
microRNA action are enacted to maintain and preserve muscle. This review article focuses on epigenetic controls on muscle metabolism that regulate MRD to avoid
muscle atrophy and support winter survival in model species of hibernating mammals,
anoxia-tolerant turtles and freeze-tolerant frogs. Such research may lead to human applications including muscle-wasting disorders such as
sarcopenia, or other conditions of limited mobility.