Energetics
Speed generally governs gait selection, with quadrupedal mammals moving from a walk to a run to a gallop as speed increases. Each of these gaits has an optimum speed, at which the minimum calories per meter are consumed, and costs increase at slower or faster speeds. Gait transitions occur near the speed where the cost of a fast walk becomes higher than the cost of a slow run. Unrestrained animals will typically move at the optimum speed for their gait to minimize energy cost.
Read more about this topic: Gait