8.4 Joint loads

Under Joint loads in the Exertion window (Figure 37), Ergoniza Intelligent displays the X, Y, and Z components of the resultant force and moment acting at each joint under the analysis conditions. Forces are expressed in newtons and moments in newton-meters.

By default, forces and moments are expressed relative to the model reference system (see Section 3.2). The text on the button at the top left of the table indicates the system currently in use. Pressing Model changes the representation to the global reference system (see Section 3.1), and the button then displays Global; pressing it again restores the model reference system. When the model is rotated about the vertical axis, the horizontal X and Y components expressed in the global reference system may change, while the Z axis continues to represent the vertical direction.

The sign of each component indicates the direction of the force or moment relative to the axes of the selected reference system. In a limb supported on the floor, the Z component of the joint forces is usually negative because the displayed internal resultant must balance the upward reaction at the support after accounting for the weights of the segments below each joint.

When a limb is unsupported, no floor reaction is transmitted through it. In this situation, the Z component of its joint forces may be positive because the proximal joints must support the weight of the distal segments and any loads applied to them.

The sign indicates only the direction of the resultant under the convention used and must not be interpreted by itself as a measure of muscular exertion or ergonomic risk. Muscular demand is assessed primarily from joint moments and the corresponding percentage exertion indicators.