Abstract: The present invention relates to a pharmaceutical composition, a food composition, and a food additive for the prevention and treatment or improvement of muscle loss, muscle weakness, and muscle atrophy, which contain Enterococcus faecalis, particularly Enterococcus faecalis EF-2001 among others, a culture solution thereof, or a killed body thereof as an active ingredient. Killed Enterococcus faecalis EF-2001 of the present invention exhibits a remarkable treatment effect for muscle loss, muscle weakness, and muscle atrophy by inhibiting the damage to muscle cells induced by oxidative stress, and thus killed lactic acid bacterium Enterococcus faecalis EF-2001 of the present invention or a culture solution thereof can be usefully used as an active ingredient in a pharmaceutical composition, a food composition, and a food additive for prevention of muscle atrophy and sarcopenia.