Differences in trunk rotation angle between bar-holding and crossed-arms positions in a seated position.

Abstract

As trunk rotation is essential for sports requiring spinal mobility, accurate assessment is important for identifying functional deficits and evaluating performance. This study compared trunk rotation angles and left-right asymmetry between bar-holding and crossed-arms positions. Twenty-four athletes performed seated trunk rotation under two conditions: (1) a bar-holding position (bar resting on shoulders), which allows shoulder girdle contribution, and (2) a crossed-arms position, which minimizes it. A ceiling-mounted camera captured overhead images. Markers attached to the acromion and posterior superior iliac spines were used to track trunk and pelvic movement, respectively. Rotation angles were calculated relative to the horizontal reference line. Each angle was measured three times per condition and averaged for analysis. Trunk rotation angles were significantly greater in the bar-holding condition than in the crossed-arms condition (right: 58.0 ± 12.9° vs. 49.2 ± 10.1°; left: 55.9 ± 12.3° vs. 47.5 ± 9.6°; p < 0.01). High positive correlations were found between conditions for both right (r = 0.82, p < 0.01) and left rotation angles (r = 0.65, p < 0.01). Asymmetry patterns were also positively correlated between conditions (r = 0.64, p < 0.01). The larger angles in the bar-holding condition confirm that shoulder girdle motion contributes substantially to the measured trunk rotation. However, the consistent asymmetry patterns suggest that either posture is valid for identifying side-to-side imbalances. This study highlights that the choice of upper limb position substantially influences the measured range of trunk rotation. Collectively, these findings emphasize that clinicians should select the specific test position based on the evaluation purpose-whether to isolate thoracic motion or to assess coordinated trunk-shoulder movement.