The output angles for all joints are calculated from the YXZ Car= dan angles derived by comparing the relative orientations of the segments p= roximal (parent) and distal (child) to the joint.

The knee angles are calculated from the femur and the Untorsioned tibia = segments, while the ankle joint angles are calculated from the Torsioned ti= bia and the foot segment.

In the case of the feet, because they are defined in a different orienta= tion to the tibia segments, an offset of 90 degrees is added to the flexion= angle. This does not affect the Cardan angle calculation of the other angl= es because the flexion angle is the first in the rotation sequence.

The progression angles of the feet, pelvis, thorax and head are the YXZ = Cardan calculated from the rotation transformation of the subject's progres= sion frame for the trial onto each segment orientation.

The following topics provide further details.

- Angle definitions
- Plug-in = Gait kinematic variables
- Upper body angles as output from Plug-in Gait
- Lower body angles as output from Plug-in Gait