Fig. 3. Observed range of gait-transition speeds plotted against the metabolically optimal transition speed for the different-sized horses. Horses switched from a walk to a trot at speeds corresponding to the optimal metabolic transition speed (i.e. the speed at which the cost of transport for walking intersects that for trotting). The top of the bars are the slowest speeds that the horses trotted at for 1 min, and the bottom of the bars are the fastest speeds that the horses walked at continuously for 1 min. Therefore, the bars represent the observed range of speeds in which the horses spontaneously switched between walking and trotting. Top and bottom error bars are 1 S.D. Our method of extrapolating polynomial curve fits for several of the horses' data produces some error in determining the optimal metabolic transition speed. This error, however, is likely to be only about a quarter the magnitude of the observed transition speed range (i.e. the vertical bar). Dashed line is the line of identity.