7.6 Hip supports

Ergoniza Intelligent detects whether the pelvis is supported on the floor in the area of the ischial tuberosities, as shown in Figure 29. When this occurs, the method used to calculate the reactions at the supports is modified in a manner similar to that described for the knees in Section 7.5. In this case, the rear supports are located at the pelvic contact areas—referred to as hip supports—and the front supports at one contact area on each foot.

The limitations described for knee supports also apply to hip supports. The coefficient of friction used to calculate possible slipping is the same as that defined for the contact between the sole of the footwear and the floor. In addition, only two support areas can exist on each side of the body. Therefore, if the hip and foot of the same leg are in contact with the floor, the hip and only one area of the foot are considered. When both the heel and forefoot are supported, the program retains the heel as the support area; if only the forefoot is supported, it uses the forefoot. This simplification generally does not represent a significant limitation, because a posture involving simultaneous contact of the hip, heel, and forefoot on the same side would be extremely forced and uncommon.

As with the knees, the reaction force exerted by the floor on the pelvis must not be confused with the internal reaction at the hip joint. The calculation of joint loads when hip support is present is explained in Section 8.2.2.5.