Fig. 2. Mechanical and energetic properties of trotting animals at the preferred trotting speed plotted versus body mass on logarithmic scales. Open circles are mean experimental values, and filled circles are model predictions. Least-squares regression lines are fitted to the model results (see text for equations). (A) Vertical stiffness, k_vert. (B) Limb angle from the vertical at touchdown. (C) Peak vertical ground-reaction force. (D) Metabolic cost of transport. Animal data are adapted with permission from Farley et al. (1993) (A-C) and from Taylor et al. (1970, 1982) (D). Data include measurements from horses, goats, dogs and rats.