A composition for strengthening, developing, differentiating, or regenerating muscle, or preventing, ameliorating, or treating muscle loss or muscle fatigue includes a Schizonepeta tenuifolia extract as an effective component. The Schizonepeta tenuifolia extract as an effective component has the effects of restoring the viability of muscle cells, increasing the endurance time on the rotarod performance test, i.e., the holding time without falling off from the rod, compared to the control group, reducing the content of LDH, AST, and ALT in blood, increasing the grip strength, enhancing the expression amount of energy metabolism-related genes in muscle tissues, increasing the density of muscle fibers in muscle tissues, inducing a change in the fibroblast arrangement to have a well-organized structure, and reducing the expression of MuRF1 in muscle tissues, as compared to the control group.