## 2 Materials and Methods
### Procedures
#### 2.2.2 Kinematics  
Shoulder kinematics, including the movements of the upper arm and shoulder girdle, were recorded using a 6-degrees-of-freedom electromagnetic tracking device (FASTRAK, Polhemus Inc., Colchester, VT, USA; Motion Monitor v9 software, Innovative Sports Training, Inc., Chicago, IL, USA). The system operated at a sampling rate of 30 Hz per sensor. The accuracy (root mean square) of this system is 0.3-0.8 mm for position and 0.15\({}^{\circ}\) for orientation when the sensor receivers are within 76 cm range of the transmitter (3 SPACE FASTRAK User's Manual, Revision C. Colchester, VT; Polhemus Inc.; 2002). To capture scapular motion during arm elevation/depression, test-retest reliability and agreement parameters of the FASTRACK system are, good to excellent when measurements are taken at close intervals (standard error of the measurement (SEM) ranges = (0.9\({}^{\circ}\)-2.2\({}^{\circ}\)); intraclass correlation coefficients (ICC) ranges = (0.76-0.99)) [28], and fair to excellent, when data is acquired one week apart (SEM ranges = (1.4\({}^{\circ}\)-4.9\({}^{\circ}\)); ICC ranges = (0.22-0.92)) [29]. Participants were seated upright on a standard chair for the palpation and digitization of specific anatomical landmarks using a sensor connected to a stylus. This process was conducted to construct the local coordinate systems (LCS) for the trunk, scapula, and humerus, as defined by the International Society of Biomechanics [30]. To establish these coordinate systems, three additional sensors were meticulously positioned. One sensor was firmly affixed to the skin overlying the spinous process of the 3 rd thoracic vertebra, defining the trunk LCS. Another sensor was securely attached to the superior surface of the acrom using double-sided tape, reinforced with sports tape, marking the scapula LCS. The third sensor was wrapped around the distal end of the arm with a 3 mm neoprene cuff, establishing the humerus LCS. An example of electromagnetic sensors positioning and attachments is provided in Figure 2.  
Figure 2: Disposition of the trunk, scapula, and humerus electromagnetic sensor receivers on a subject. With these sensors in place, participants then executed the arm elevation and depression tasks they had previously practiced (Figure 1a-d). During data collection session, two clinical researchers ([PERSON] and [PERSON]) conducted all digitisations and provided standardized instructions, while a third researcher ([PERSON]) operated the computer. Subsequently, joint angles were calculated and expressed as Euler angle decompositions, describing the relative orientation of the scapula with respect to the thorax. The coordinate system for scapular rotations was defined with the \(y\)-axis pointing upward, the \(x\)-axis extending from left to right, and the \(z\)-axis pointing backward. The \(Y\)X'Z'' Euler sequence was employed to convey scapular orientation, with the first rotation representing internal (positive)/external rotation (IR/ER) of the scapula along the \(y\)-axis, the second rotation signifying upward (negative)/downward rotation (UR/DR) around the twice-rotated scapular \(x\)-axis, and the third rotation indicating anterior (negative)/posterior tilting (AT/PT) around the rotated scapular \(z\)-axis. Data were filtered using a lowpass 8 Hz Butterworth filter, exported to MATLAB (MathWorks Inc., Natick, MA, USA, vR2016a) and then reduced to increments of 15\({}^{\circ}\) from minimum (initial position) to 120\({}^{\circ}\) of humero-thoracic (HT) elevation (final position). For presentation and clinical interpretability purposes, scapular upward rotation was multiplied by \(-1\) (thereby later shown as positive in Figure 4). Left-handed, rotations of the left side were transformed by appropriate geometrical calculation for projection on the right side. Repetitions of each task were averaged for ulterior analysis. For PNF-D2-flx/ext (Figure 1a), repetitions 1 and 5 were removed, having been averaged repetitions 2-4.