ABSTRACT
The iliocostalis lumborum, longissimus thoracis and spinalis thoracis muscles were studied electromyographically in six male individuals between 18 and 23 years old. They were connected to co-axial needle electrodes while in orthostatic, kneeling and sitting positions performing movements of flexing, extending and rotating the trunk. In the total flexing of the trunk the muscles did not present any action potential. The results showed intense potential for action while flexing the trunk 45 degrees, extending the trunk beginning at 45 degrees of flexing and in homolateral rotation for the muscles analyzed in the orthostatic position, emphasizing the iliocostalis lumborum muscle in the extension of the trunk which registered very strong action potentials in all individuals. There were similar results for movements of flexing and extending the trunk in the kneeling position, emphasizing the longissimus thoracis muscle in the movement of hyperextension. In the sitting position the more intense potentials were for the movements of extension, flexing with rotation and homolateral rotation of the trunk, emphasizing the longissimus thoracis muscle with strong potentials.