FUNCTION OF THE INTERCOSTAL MUSCLES IN TROTTING DOGS - VENTILATION ORLOCOMOTION

Although the intercostal muscles play an important role in lung ventil ation, observations from fishes and ectothermic tetrapods suggest that their primary function may be locomotion, To provide a broader unders tanding of the role these muscles play in locomotion, I measured venti latory airflow at the mouth and activity of the fourth and ninth inter costal muscles in four dogs trotting on a treadmill, During rest and t hermoregulatory panting, activity of the intercostal muscles was assoc iated with inspiratory and expiratory airflow, However, during trottin g, activity of the interosseous portions of the intercostal muscles wa s correlated with locomotion, When ventilation and stride cycles were not synchronized, activity of the interosseous intercostal muscles sta yed locked to the locomotor events and drifted in time relative to ven tilation, In contrast, activity of the parasternal portion of the inte rnal intercostal muscles was always associated with inspiratory airflo w, These observations suggest that, in dogs, locomotion is the dominan t function of the interosseous portions of the intercostal muscles, Ho wever, the parasternal intercostal muscles are primarily inspiratory i n function.