Muscle atrophy is one of the main deleterious consequences of ageing, diseases (e.g. cancers and AIDS), and physical inactivity. It is especially detrimental to locomotion, heat production, and metabolism thus leading to frailty, increased dependency and metabolic disorders. Apart from being a major clinical problem for older people, muscle loss is also observed during physical inactivity, which has become a major leading cause of death worldwide. Although basic knowledge regarding the underlying mechanisms of muscle atrophy is continuously growing, essentially from rodent models and clinical trials in humans, there are still no efficient therapeutic strategies for its prevention and treatment. Hibernating bears exhibit a strong and unique ability to preserve muscle mass in conditions of muscle disuse and food deprivation, conditions during which muscle atrophy is observed in human. Bears remain inactive in winter during up to seven months without arousal episodes (without eating, drinking, urinating or defecating), with only very limited loss in muscle protein content and strength, whereas muscle and fibre cross-sectional area are preserved. Underlying mechanisms have not been understood yet, but our approaches combine molecular and cellular studies of bear muscle as well as human muscle cells exposed to bear serum. Our recent demonstration of trans-species effects of bear serum controlling protein degradation in cultured human muscle cell holds promising potential. Hence, exploration of winter bear serum therefore holds potential for developing new tools to fight human muscle atrophy and related metabolic disorders.