5.1 Segments and joints

The biomechanical model implemented in Ergoniza Intelligent divides the entire body into 16 main segments (shown in black in Figure 6). In this count, the head and neck constitute two distinct subsegments in the kinematic chain, although certain biomechanical calculations treat them together as a single functional head-neck segment.

These segments are supplemented by two segments in each thumb, three in each of the other fingers, and two representing the toes of each foot. These additional segments form part of the articulated graphical representation but are not involved in every biomechanical calculation.

Figure 6 also shows fourteen main joints, represented in blue. Some joint levels used in specific calculations are not shown separately in the figure, such as the joint between the C1 vertebra and the skull or the L4/L5 intervertebral level.

In general, each segment is bounded by two joints. Exceptions are the pelvis, which connects the two hips to the L5/S1 lumbosacral joint, and the torso, which connects L5/S1 to the shoulders and the C7/T1 region.

In the model's neutral position, the joint centers of the hips, knees, and ankles lie in the frontal plane. The L5/S1 joint is located slightly behind this plane because of the configuration adopted for the lumbosacral joint, described in Section 5.1.2.1. Consequently, the joints located above L5/S1 also lie slightly behind the frontal plane.

The segments are considered rigid, and the joints are modeled as points located at their respective joint centers. Each segment's longitudinal axis begins and ends at a joint. The center of gravity of each segment is considered to lie on its longitudinal axis, except for the foot.