Evaluation of animal models for the study of exercise-induced muscle enlargement. Skeletal muscle is known to enlarge in response to high-resistance training programs in humans. Study of the cellular mechanisms of muscle enlargement and the adaptations of muscle to strength-training programs has been difficult because of the need to analyze entire muscles. This precludes the use of human subjects in many experiments of this nature. Several animal models have been developed for the study of muscle enlargement; these models basically fall into three categories: 1) stretch hypertrophy, 2) compensatory hypertrophy, and 3) exercise-induced hypertrophy. This review attempts to analyze these models as models of muscle enlargement produced by strength training in humans. Three areas must be considered when evaluating animal models of human muscle enlargement produced by strength training: 1) response topography, 2) magnitude of enlargement, and 3) muscle fiber adaptations produced as a result of the enlargement. Based on these considerations, it is concluded that none of the animal models currently in use truly represents the human strength-training situation under all conditions. All three models, however, provide valuable information about the plasticity of skeletal muscle in response to a broad spectrum of muscle enlargement. 