Abdominal Muscles Activities during Isometric Forward and Downward Pushing Tasks by the Arms in the Sitting Position

Abstract

[Purpose] We investigated the trunk muscles, activities for stabilizing the spine against load by arm movement. [Subjects] Eight male subjects participated in this study. [Methods] Subjects performed 1) a pushing forward task (load perpendicular to the trunk) and 2) a pushing downward task (load parallel to the trunk) at different load magnitudes with isometric arm extension. Electromyography (EMG) of rectus abdominis (RA), oblique internus abdominis (OI), oblique externus abdominis (OE), lumbar mutifidus (LM), and longissimus thoracis (LT) were recorded with surface electrodes. [Results] Activity of RA, OE and OI increased with load magnitude in both tasks. RA was influenced by load direction. The activity of RA in the downward pushing task was larger than in the forward pushing task. Activities of LM and LT were influenced by load magnitude, but these muscles activities were low. [Conclusion] The RA muscle is the only muscle influenced by direction of load to the trunk.