Influence of Multiplanar Shoulder Position on Transverse-Plane Torque Generation Capacity

This study evaluated the influence of three-dimensional shoulder positioning on internal (IR) and external (ER) rotator muscle strength. Ten young adults were tested at full IR, full ER, and three interpolated angles between these extremes, across two arm elevation positions (45° and 90° in the scapular plane). Maximal torque and optimal angles for IR and ER were determined using second-order polynomial regression. We hypothesized that the optimal angles for IR and ER torque production do not coincide, and that the ERlIR torque ratio peaks at the optimal ER angle and reaches its minimum at the optimal IR angle in both positions. Additionally, we expected that arm elevation would influence torque ratios. The results showed a 30° difference between the optimal IR and ER angles, with significant differences in ERlIR ratios (p = 0.012) exclusively in the 45° elevation position. However, no significant differences in ERlIR ratios were found between the optimal IR angle and full ER, or between the optimal ER angle and full IR (p > 0.315) in either position. IR torque at the optimal IR angle was significantly higher in the 45° elevation position (median = 34.3 Nm) compared to the 90° elevation position (median = 31.3 Nm; p = 0.027). Despite this, arm elevation in the scapular plane did not significantly affect ERlIR ratios at any tested angle (p > 0.105). These findings suggest that ERlIR torque ratios are relatively stable across different shoulder configurations and are largely independent of arm elevation.