[Electromyographic activity of neck muscles during the production of inspiratory pressure]

The differential inspiratory EMG activities of the scalene (SCLN), sternocleidomastoid (STERNO), and trapezius (TRAPEZ) muscles were studied in 6 awake and healthy men (mean age, 22 years; and mean weight, 62.4 kg). Pairs of fine wire EMG electrodes were inserted into each of these muscles using a guide needle and high-resolution ultrasonography. With subjects on a mouthpiece, inspiratory effort against an occluded airway was recorded at end expiratory position in the standing position. Mouth pressure and integrated EMG signals were sampled to a computer during the gradual production of maximal static inspiratory pressure (PImax) over 10 s. Maximum EMG activity (EMGmax) was obtained for each muscle during specific respiratory and postural maneuvers. Mouth pressures and integrated EMG activities were expressed as percentages of PImax and EMGmax, respectively. As mouth pressure increased, SCLN, then STERNO, and finally TRAPEZ EMGs were sequentially activated in 5 subjects. In one subject, STERNO preceded SCLN EMG activation. Group mean (+/- SE) mouth pressures at the onset of SCLN, STERNO, and TRAPEZ EMG were 10.3 +/- 5.8% PImax. 30.8 +/- 8.2% PImax, and 79.3 +/- 9.6% PImax, respectively. TRAPEZ mouth pressures differed from SCLN and STERNO values (p < 0.05). At 90% PImax, group mean (+/- SE) SCLN, STERNO, and TRAPEZ EMG activity reached 69.7 +/- 9.0% EMGmax, 51.5 +/- 11.1% EMGmax, and 5.1 +/- 2.4% EMGmax, respectively. TRAPEZ EMG at 90% PImax differed from both SCLN and STERNO values (p < 0.05). These results suggest that SCLN has strong, STERNO intermediate, and TRAPEZ weak, inspiratory activities.