Effect of forearm positions on scapular movements and trunk rotation angles.

[Purpose] The study investigated the impact of distinct forearm positions on scapular movement and trunk rotation angles. [Participants and Methods] We enrolled 23 healthy young males. Measurements of trunk rotation and relative scapular segment angles were acquired under three conditions employing three-dimensional motion analysis, each executed in a seated posture: (1) both forearms in a neutral position, (2) the forearm on the rotational side adopted supination while the opposite forearm utilized pronation, and (3) the forearm on the rotational side employed pronation while the opposite forearm assumed supination. [Results] The scapular angles in all three scenarios reflected downward rotation, posterior tilt, and external rotation of the rotational-side scapula. Conversely, the contralateral scapula exhibited upward rotation, anterior tilt, and internal rotation. Although the scapular and trunk rotation angles corresponded with the three forearm positions, all three were significantly different and were significantly increased when the rotational-side forearm was in supination (opposite side pronation) and decreased when the rotational-side forearm was in pronation (opposite side supination). [Conclusion] During trunk rotation, regular scapular movements were observed, which varied depending on forearm position and influenced the range of trunk rotation.