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Craniomandibular electromyographic (EMG) studies frequently include several parameters, e.g. resting, chewing and tooth-clenching. EMG activity during these parameters has been recorded in the elevator muscles, but little is known about the respiratory muscles. The aim of this study was to compare EMG activity in obligatory and accessory respiratory muscles between subjects with different breathing types. Forty male subjects were classified according to their breathing type into two groups of 20 each: costo-diaphragmatic breathing type and upper costal breathing type. Bipolar surface electrodes were placed on the sternocleidomastoid, diaphragm, external intercostal and latissimus dorsi muscles. EMG activity was recorded during the following tasks: (i) normal quiet breathing, (ii) maximal voluntary clenching in intercuspal position, (iii) natural rate chewing until swallowing threshold, (iv) short-time chewing. Diaphragm EMG activity was significantly higher in the upper costal breathing type than in the costo-diaphragmatic breathing type in all tasks (P < 0.05). External intercostal EMG activity was significantly higher in the upper costal breathing type than in the costo-diaphragmatic breathing type in tasks 3 and 4 (P < 0.05). Sternocleidomastoid and latissimus dorsi EMG activity did not show significant differences between breathing types in the tasks studied (P > 0.05). The significantly higher EMG activity observed in subjects with upper costal breathing than in the costo-diaphragmatic breathing type suggests that there could be differences in motor unit recruitment strategies depending on the breathing type. This may be an expression of the adaptive capability of muscle chains in subjects who clinically have a different thoraco-abdominal expansion during inspiration at rest. [ABSTRACT FROM AUTHOR]