Chest wall motion is highly correlated to lung volume, which is critical for normal pulmonary function. Therefore’ maintaining proper chest wall expansion capacity is vital. The aim of the study was to quantify the immediate effects of arm abduction synchronized with breathing movement on the chest wall motion and activities of selective inspiratory muscles during maximal inspiration. Twenty healthy males participated in the study’ each performing maximal inspiration with and without synchronized arm abduction. The motion of the upper thorax’ lower thorax’ and abdomen compartments’ and the activities of the sternocleidomastoid and costal diaphragm muscles were measured simultaneously. The results showed that synchronized arm abduction increased the muscle activities and the normalized magnitude and rate of volume change of the upper thorax’ while those of the abdomen compartment were decreased. However’ synchronized arm abduction does not affect the total volume changes. This suggests that synchronized arm abduction helped increase the demand of the muscles and the expansion of the upper thorax without affecting the total volume change of the overall chest wall during maximal inspiration.