Effect of arm lifts on the center of pressure in quiet standing

Abstract

Background and aim: This study examines what effect arm lifts have on the movement of the center of pressure (COP) during quiet standing. Questions that were investigated were; is there evidence of Anticipatory Postural Adjustments (APA) in the opposite direction of upcoming arm movements and where is the COP positioned at the end of the arm lift?

Methods: A 500 Hz ProReflex motion capture system and AMTI force platform were used to capture the participants’ unilateral and bilateral arm lifts in the diagonal, forward, and sideways direction. These measurements allowed for the APA and COP Arm Horizontal variables to be calculated.

Results: The results indicated that there was no evidence for APA in the opposite direction of the upcoming arm movements. Before lifting one arm sideways the participants leaned in the same direction as the upcoming arm lift. When the arms had reached their horizontal position, the COP was typically positioned in the forward direction. The COP was positioned further away from the baseline when the lifting had occurred in the diagonal and forward directions than in the sideways direction. When one arm had reached the horizontal position when lifting sideways, the COP was positioned in the same direction as the arm lift.

Discussion: In contrast to prior studies, APA was in the same direction as the upcoming arm movement. As expected, the participants leaned in the forward direction when both arms had reached their horizontal position. The participants leaned in the same direction as the previous arm lift when only one arm was lifted in the sideways direction. Further analyses could focus on the COP movements during the arm lifts. The study can be extended to investigating how postural control is affected in other age groups and patient groups.