Figure 2.

Postures used in the study: All handles were adjusted to the vertically rested elbow height (when the arm was resting vertically by the side of the body). Subjects were seated and grasped a handle (a). Different arm postures (flexed (a) vs. extended (b) elbow) for pull were examined. Pull and vertical force exertions at the hand (F_z and F_y, respectively) result in external moments applied at each joint (M_{elbow, external}, M_{shoulder, external}) via moment arms (y_elbow-hand, y_{shoulder-hand}, z_elbow-hand,, z_{shoulder-hand}). All three direction forces (F_x, F_y, F_z) were measured using a lode cell.