摘要
Pushing objects in the presence of body asymmetries could increase the risk of back injury. Furthermore, when the object is heavy, it could exacerbate the effects induced by asymmetrical posture. We investigated how the use of asymmetrical posture and/or upper extremity movement affect vertical torque (T z ) and center of pressure (COP) displacement during pushing. Ten healthy volunteers were instructed to push objects of three different weights using two hands (symmetrical hand use) or one hand (asymmetrical hand use) while standing in symmetrical or asymmetrical foot-positions. The peak values of T z and COP displacement in the medial-lateral direction (COP ML ) were analyzed. In cases of isolated asymmetry, changes in the T z were mainly linked with effects of hand-use whereas effects of foot-position dominated changes in the COP ML displacement. In cases of a combined asymmetry, the magnitudes of both T z and COP ML were additive when asymmetrical hand-use and foot-position induced the rotation of the lower and upper body in the same direction or subtractive when asymmetries resulted in the rotation of the body segments in the opposite directions. Moreover, larger T z and COP displacements were seen when pushing the heavy weight. The results point out the importance of using T z and COP ML to describe the isolated or combined effects of asymmetrical upper extremity movement and asymmetrical posture on body rotation during pushing. Furthermore, it suggests that a proper combination of unilateral arm movement and foot placements could help to reduce body rotation even when pushing heavy objects.