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Hypaxial muscle activity during running and breathing in dogs

Stephen M. Deban^* and David R. Carrier

Department of Biology, University of Utah, Salt Lake City, UT 84112, USA

View larger version (35K): [in a new window]   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.

View larger version (34K): [in a new window]   Fig. 3. Ensemble averages of electromyographic (EMG) activity of the external intercostal muscle. The pattern of bursting in uncoupled breath averages is similar in all dogs, and its relationship to ventilation reveals an inspiratory function for this muscle. The pattern of activity averaged relative to the stride is more variable, but a clear bursting pattern is present, indicating a locomotor function. Samples are from four dogs (A—D), and the average across four dogs (E), with ventilatory (bold lines) and acceleration (thin lines) traces to reveal relationships to breath and stride (F). IF indicates ipsilateral forelimb support and CF contralateral forelimb support in the footfall bars at the bottom. All traces are on the same time scale. Exp., expiration; Insp., inspiration.

View larger version (30K): [in a new window]   Fig. 2. Ensemble averages of electromyographic (EMG) activity of nine trunk muscles from a single dog standing and panting, revealing a ventilatory function for all muscles except the longissimus dorsi and deep pectoralis. Only the external intercostal and parasternal internal intercostal have an inspiratory function. Muscles that were active were not all active at the same time. Ventilatory airflow traces are shown below for reference. Exp., expiration; Insp., inspiration. All traces are on the same time scale. See text for discussion.

View larger version (32K): [in a new window]   Fig. 4. Ensemble averages of electromyographic (EMG) activity of the internal intercostal muscle. The patterns are similar for all dogs, indicating an expiratory function as well as a locomotor function. Samples are from four dogs (A—D), and the average across four dogs (E), with ventilatory (bold lines) and acceleration (thin lines) traces to reveal relationships to breath and stride (F). IF indicates ipsilateral forelimb support and CF contralateral forelimb support in the footfall bars at the bottom. All traces are on the same time scale. Exp., expiration; Insp., inspiration.

View larger version (38K): [in a new window]   Fig. 5. Ensemble averages of electromyographic (EMG) activity of the parasternal portion of the internal intercostal muscle. The bursting pattern is consistent in uncoupled breath averages, indicating a clear inspiratory function for this muscle. The bursting is much more variable in uncoupled stride averages and almost undetectable in the average across all dogs (E), indicating a variable or sporadic locomotor function that may be different in each dog. Samples are from four dogs (A—D), and the average across four dogs (E), with ventilatory (bold lines) and acceleration (thin lines) traces to reveal relationships to breath and stride (F). IF indicates ipsilateral forelimb support and CF contralateral forelimb support in the footfall bars at the bottom. All traces are on the same time scale. Exp., expiration; Insp., inspiration.

View larger version (33K): [in a new window]   Fig. 6. Ensemble averages of electromyographic (EMG) activity of the thoracic portion of the external oblique muscle. This muscle clearly functions in both ventilation and locomotion, and the bursting pattern is consistent among dogs in both uncoupled stride and breath averages. Bursting starting at peak inspiratory airflow and extending to peak expiratory airflow reveals an expiratory function for this muscle. Samples are from four dogs (A-D), and the average across four dogs (E), with ventilatory (bold lines) and acceleration (thin lines) traces to reveal relationships to breath and stride (F). IF indicates ipsilateral forelimb support and CF contralateral forelimb support in the footfall bars at the bottom. All traces are on the same time scale. Exp., expiration; Insp., inspiration.

View larger version (33K): [in a new window]   Fig. 7. Ensemble averages of electromyographic (EMG) activity of the abdominal portion of the external oblique muscle. This muscle has a locomotor function, revealed by a consistent bursting pattern in all dogs and a clear bursting pattern in the average across dogs. A ventilatory function is not evident, given the absence of bursting in the uncoupled breath averages. Samples are from four dogs (A-D), and the average across four dogs (E), with ventilatory (bold lines) and acceleration (thin lines) traces to reveal relationships to breath and stride (F). IF indicates ipsilateral forelimb support and CF contralateral forelimb support in the footfall bars at the bottom. All traces are on the same time scale. Exp., expiration; Insp., inspiration.

View larger version (37K): [in a new window]   Fig. 8. Ensemble averages of electromyographic (EMG) activity of the abdominal portion of the internal oblique muscle. As in Fig. 7, this muscle has a locomotor function but no ventilatory function during running. Samples are from four dogs (A-D), and the average across four dogs (E), with ventilatory (bold lines) and acceleration (thin lines) traces to reveal relationships to breath and stride (F). IF indicates ipsilateral forelimb support and CF contralateral forelimb support in the footfall bars at the bottom. All traces are on the same time scale. Exp., expiration; Insp., inspiration.

View larger version (36K): [in a new window]   Fig. 9. Ensemble averages of electromyographic (EMG) activity of the transversus abdominis muscle. This muscle shows clear bursting in all ensemble averages, consistently across dogs, indicating both a ventilatory and locomotor function. The pattern of activity relative to the ventilatory cycle reveals an expiratory function for this muscle. Samples are from four dogs (A-D), and the average across four dogs (E), with ventilatory (bold lines) and acceleration (thin lines) traces to reveal relationships to breath and stride (F). IF indicates ipsilateral forelimb support and CF contralateral forelimb support in the footfall bars at the bottom. All traces are on the same time scale. Exp., expiration; Insp., inspiration.

View larger version (29K): [in a new window]   Fig. 10. Ensemble averages of electromyographic (EMG) activity of the deep pectoralis muscle. This muscle has a clear locomotor function that is consistent between dogs, but no ventilatory function. Samples are from two dogs (A and B), and the average across two dogs (C), with ventilatory (bold lines) and acceleration (thin lines) traces to reveal relationships to breath and stride (D). IF indicates ipsilateral forelimb support and CF contralateral forelimb support in the footfall bars at the bottom. All traces are on the same time scale. Exp., expiration; Insp., inspiration.

View larger version (31K): [in a new window]   Fig. 11. Ensemble averages of electromyographic (EMG) activity of the longissimus dorsi, revealing a consistent locomotor function but no ventilatory function. Samples are from three dogs (A-C), and the average across three dogs (D), with ventilatory (bold lines) and acceleration (thin lines) traces to reveal relationships to breath and stride (E). IF indicates ipsilateral forelimb support and CF contralateral forelimb support in the footfall bars at the bottom. All traces are on the same time scale. Exp., expiration; Insp., inspiration.