2.3. Experimental procedure
2.3.1. Kinematics
The transmitter was fitted on a rigid plastic frame 30 cm in front of the subject and established the global coordinate system (GCS). The X-axis was horizontal, pointing for- ward; the Y-axis was vertical, pointing upward; and the Z-axis was horizontal, pointing left to right. Three Polhe- mus sensors were attached to each subject (Fig. 1). The sur- face electromagnetic sensors were fixed to the skin overlying the sternum and the flat surface on the superior