The effect of posture on the role of pectoralis major and latissimus dorsi muscles in expiration in tetraplegia

Abstract

This study was designed to. examine the effect of posture on forced expiration as reflected in phasic electromyographic activity in accessory expiratory muscles in tetraplegic subjects with complete lesions between the fifth and eight cervical segments. In order to determine the effect of posture on the action of the clavicular head of the pectoralis major muscle and the latissimus dorsi muscle during forced expiration, the subjects were studied in two test positions, support sitting and supine lying. Electromyographic examination of the above mentioned muscles in eight tetraplegic subjects showed changes in electrical activity in the clavicular portion of the pectoralis major muscle when the subjects were studied in the supine position. Four out of eight subjects showed evidence of an increase in EMG activity in the supine lying position. When the muscle was tested with the patient in the supported sitting position it failed to demonstrate a significant increase in electromyographic activity during forced expiration. We concluded therefore that the role of the clavicular portion of the pectoralis major muscle during expiration in tetraplegia is posture dependent. These findings have important therapeutic implications: specific training programmes to increase the strength and endurance of this muscle should be conducted with the subject in the correct position. The action of the latissimus dorsi muscle was not significantly influenced by the postural changes during forced expiration.

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