Fig. 4. Average electromyographic (EMG) activity in the left fourth external intercostal muscle from four dogs trotting at intermediate speeds. Each trace represents the average rectified signal from 15 strides. The EMG signals are plotted relative to an average limb support cycle (N=5) for each dog. The phases of limb support, dog masses and running speeds are as described in Fig.2. LH, left hind, top trace; LF, left fore, second trace; RF, right fore, third trace; RH, right hind, bottom trace.