A 6-degree-of-freedom electromagnetic tracking device, the Polhemus Fastraka (SPACE FASTRAK, Colchester, VT, USA) was used for recording the kinematic data. Real-time 3-D position and orientation of the thorax, scap- ula and humerus were tracked at 30 Hz. The Polhemus Fastraka consists of a transmitter and four receivers/sen- sors, all hardwired to the system’s electronic unit. The transmitter generates a low-frequency electromagnetic field, which is detected by the sensors. The system’s elec- tronic unit determines the relative orientation and position of the sensors, and this information is sent to a computer where the data are collected. The reported root mean square (RMS) accuracy of this system is 0.3–0.8 mm for position and 0.15° for orientation when used within a 76- cm source to sensor separation (SPACE FASTRAK User’s Manuel, Revision F. Colchester, VT; Polhemus Inc.; 1993).