Factors in breathing maneuvers that affect trunk electromyogram during manual lifting.

摘要

STUDY DESIGN: A fully randomized experiment was conducted in a laboratory with a breath-by-breath monitor to control accurately the two factors of breathing maneuvers: breathholding duration and air volume within the thoracic cavity. OBJECTIVES: To resolve the controversy in previous reports about the effect of breathholding on the trunk electromyogram, and to verify the hypothesis that not only the factor of glottis closure, but also that of the air volume inside the thoracic cavity affects the trunk muscular activities during lifting. SUMMARY OF BACKGROUND DATA: Breathing was shown to affect spinal loading. However, there still is a debate about the effect of breathholding on trunk muscular activation during activities. It is possible that variations in air volume influence this effect. METHODS: Seven healthy, volunteer men participated in lifting tasks, in which lifting moment was standardized. Three breathing maneuvers were used: sustained breathholding with tidal volume of air, sustained breathholding with functional residual volume, and intended breath-nonholding involving inspiration within tidal capacity. Data on the surface electromyographic activation of the external oblique muscle, rectus abdominis, erector spinae, latissimus dorsi, air volume inside the cavity, and the duration of the one breath held in the last lift were collected and analyzed. RESULTS: Of the four muscles investigated, the breathing maneuvers affected only the external oblique muscle. The effect of sustained breathhold during lifting was the significantly increased activation of this muscle (P < 0.05). The effect of decreased air volume held was further increased activation. Intention to inspire normally during lifting decreased external oblique activation, but increased compensatory diaphragmatic effort, measured as inspiratory flow acceleration. CONCLUSIONS: Both the factors of the breathheld state and sustained air volume were verified to affect the external oblique activation during lifting. The current study emphasizes that both factors should be controlled in studies analyzing trunk electromyogram during activities. Otherwise, these breathing variations will be a confounding factor on electromyogram results.