Fig. 1. Representative electromyographic (EMG) traces from two muscles with traces for ventilatory airflow and vertical acceleration of the trunk illustrating the ensemble averaging method of analysis. The rectified EMG signal is sampled relative to ventilation in windows extending between peaks of expiratory airflow (A). In this case, the parasternal is entrained to ventilation and the bursts do not shift within the sampling window, while the bursts of the pectoralis do. The same EMG signals are also sampled relative to the stride in windows extending between peaks of vertical acceleration during contralateral forelimb support (B). Here, the pectoralis remains locked to the stride and its bursts do not shift relative to the sampling windows, but the bursts of the parasternal do. Traces in A and B are aligned in time. Footfall patterns of the forelimbs are shown at the bottom, with boxes labeled IF indicating the period of ipsilateral forelimb support and boxes labeled CF indicating contralateral forelimb support. See Materials and methods for further explanation. Exp., expiration; Insp., inspiration.