## 4 Discussion  
We specifically examined a diagonal movement pattern of arm elevation/depression (PNF-D2-flx/ext), which is distinct from traditional arm elevation/depression tasks conducted in the three standard planes of motion--shoulder abduction, shoulder flexion, and shoulder scaption-- and has its unique scapular kinematics. Although the four arm elevation tasks generally exhibited a scapular motion pattern of external rotation, upward rotation and posterior tilting (Figures 3-5) during arm movement, the scapula exhibited less upward rotation (Figure 4) and more posterior tilt (Figure 5) in PNF-D2 compared to shoulder abduction, flexion, or scaption. Particularly noteworthy was the consistent transition from internal rotation to external rotation (and vice versa) of the scapula in PNF-D2 (Figure 3a). This transition was more prominent than in shoulder flexion (Figure 3c), shoulder scaption (Figure 3d), and, to a lesser extent, shoulder abduction (Figure 3b). However, it is worth noting that differences between groups were not statistically significant across all tasks. Studies examining 3D scapular kinematics during shoulder movements beyond the conventional full or near-full arm elevation in the sagittal, frontal, and scapular plane are scarce. An early research by [PERSON] and [PERSON] [4] was among the first to compare 3D scapular kinematics between functional tasks (such as reaching for a car seat belt or reaching for an overhead shelf) and humeral elevation movements constrained to a specific plane of motion. In their study, [PERSON] and [PERSON] discovered significant differences in all scapular rotations for most task conditions, even when the humero-thoracic elevation and plane of elevation angles were the same. The functional tasks they examined, reaching for an object on the right side (\"right side\") and reaching for an object on the left side (\"left side\") with the right hand are conceptually similar, to some extent, to the functional movement task we employed in our research (i.e., PNF-D2). The authors noticed that these functional tasks resulted in larger scapular external rotation angles than the constrained task. However, for scapular upward rotation and posterior tilt, the constrained arm elevation task exhibited, on average, larger angles, with differences of up to 5.6\({}^{\circ}\) and 2.3\({}^{\circ}\), respectively. The findings of our study are somewhat in line with those of [PERSON] and [PERSON]'s research. We also observed reduced upward rotation in PNF-D2 when compared to the three constrained planes of arm elevation tasks; however, it is important to note that this difference was more pronounced at higher angles of humero-thoracic (HT) elevation (between 90\({}^{\circ}\) to 120\({}^{\circ}\)). At a 30\({}^{\circ}\) HT elevation, which corresponds to the angle [PERSON] and [PERSON] used to compare \"right side\" and \"left side\" with constrained arm elevation, PNF-D2 actually exhibited larger scapular upward rotation (mean [95%CII]) than shoulder abduction (+4.3\({}^{\circ}\) [1.7\({}^{\circ}\)-6.9\({}^{\circ}\)], \(p\) < 0.001), shoulder flexion (+4.9\({}^{\circ}\) [2.6\({}^{\circ}\)-7.1\({}^{\circ}\)], \(p\) < 0.001), or shoulder scaption (+6.0\({}^{\circ}\) [3.8\({}^{\circ}\)-8.3\({}^{\circ}\)], \(p\) < 0.001). When contrasting scapular external rotation and posterior tilting with the aforementioned study, the comparison becomes more intricate, especially concerning scapular external rotation. This complexity arises because we found significant interaction effects of HT angle \(\times\) task in both scapular rotations. At 30\({}^{\circ}\) of HT elevation, nevertheless, scapular external rotation was, on average, significantly larger in PNF-D2 than in shoulder abduction (+18.6\({}^{\circ}\) (15.0\({}^{\circ}\)-22.1\({}^{\circ}\)), \(p\) < 0.001), and shoulder scaption (+9.1\({}^{\circ}\) (5.8\({}^{\circ}\)-12.4\({}^{\circ}\)), \(p\) < 0.001), but it was comparable to shoulder flexion (+1.5\({}^{\circ}\) (\(-\)1.6\({}^{\circ}\)-4.5\({}^{\circ}\)), \(p\) > 0.05).