Abstract
[Purpose] The purpose of this study was to clarify the activities of the trunk back muscles and movement of the spine at different angles of unilateral and bilateral arm anterior elevation in a seated position. [Subjects and Methods] The subjects were 20 healthy males. Electromyograms of the multifidus, longissimus lumborum, longissimus thoracis, and iliocostalis were recorded at unilateral and bilateral arm anterior elevation angles of 30°, 60°, 90°, 120°, and 150° in a seated position. [Results] The integrated electromyogram (iEMG) value for the multifidus was significantly higher at 90° than at 30°, and significantly lower at 150° than at 30°, 60°, 90°, or 120°. The iEMG value for the longissimus lumborum was significantly higher at 150° than at 90° with bilateral arm anterior elevation. The iEMG value for the multifidus on the elevation and non-elevation sides was significantly higher at 150° than at 60° or 90° during unilateral anterior elevation. The iEMG value for the longissimus thoracis on the elevated side was significantly higher at 90° than at 150° during unilateral anterior elevation. In bilateral arm anterior elevation of 90°, posterior trunk movement was greater, and in unilateral arm anterior elevation, it deviated laterally toward the non-elevated side as the lift angle increased. [Conclusion] During unilateral arm anterior elevation, the longissimus thoracis on the elevation side is dominant. Bilateral arm anterior elevation involved the multifidus at 90°.
