Effect of Gravity on Movement and Muscle Characteristics for Daily Occupational Performance in Sitting and Side-Lying Positions in Adults

Abstract

The purpose of this study was to compare differences in the activation of biceps and triceps, if any, in patients with stroke in a simple reaching and grasping task under two body orientations, one performed under constant gravity and the other against gravity. Twenty healthy adults from the midwestern United States were randomly assigned to either an against gravity (sitting) or a constant gravity (side-lying) body orientation in a within-subject repeated measure design. Each participant performed the task of moving a filled soda can from a fixed start and end position. The results showed that the reaching velocity was significantly lower ( p < .0001) and muscle activations of biceps and triceps as measured by surface electromyography were significantly less pronounced ( p < .00001) in the side-lying position compared to the sitting position. The data suggest that the muscle activation patterns differ under different biomechanical constraints created by different gravity situations. Thus, the same functional task done in different body orientations may not necessarily fully recruit the same muscle groups in all orientations.