Fig. 4. Mean ground reaction force data for a trotting dog. Data from one step are repeated so that the general pattern may be more easily seen. These data represent the resultant force trace of both limbs, as opposed to single-limb forces, and are averaged from 15 trials of force-plate data. The trace of the large single peak during a step is the vertical (vert.) force. The trace that first drops below and then rises above baseline is the recording of the fore–aft force. The very flat, unlabeled trace is the recording of the lateral force. The average speed of this animal trotting across the force plate was 2.0ms^-1.