maximum running speed limitations on terrestrial mammals a theoretical approach here we study maximum running speed mrs limitations on a previously proposed model of energetic and muscletendon unit functions on running mammals in the present work the mrs and some anatomical or physiological limitations are estimated for mammals with body mass between 15 and 300 kg the mrs variations with body mass are discussed and compared with results of previous experimental and observational studies the tendon strength seems to be the most relevant limitation but leg extensor muscle mass and metabolic costs could be relevant also the physiological maximum muscle speed seems to be less important in the body mass range studied here