Abstract
This study aims to investigate how varying shoulder movement speeds affect spinal mobility to enhance understanding of the trunk's adaptive response to these perturbations. Eleven healthy participants were fitted with motion markers placed on the bilateral shoulders, upper extremities, and the spinous processes of the 8th thoracic vertebra (T8), 4th lumbar vertebra (L4), and the posterior superior iliac spine, representing the 2nd sacral vertebra (S2). Each participant performed bilateral forward shoulder elevation in the sagittal plane at three different speeds (natural, fast, and slow) in a randomized order. Each speed condition included five repetitions, with the middle three repetitions used for analysis. The peak-to-peak displacement and excursion of T8, L4, and S2 during the ascending and descending phases of shoulder elevation were recorded. Repeated measures one-way analysis of variance (ANOVA) and the Friedman test were applied to compare the effects of the three speeds. Significant differences were observed between the fast and slow speeds in the peak-to-peak displacements of T8 and L4 during the descending phase, as well as in the T8 excursion across the full range of forward shoulder elevation, or 31%, 24%, and 26% increase, with p-values of 0.045 (ES = 1.053), 0.042 (ES = 1.019), and 0.028 (ES = 1.174), respectively. No significant differences were detected at the S2 level. Spinal mobility during forward shoulder elevation was observed at fast speed, especially during the descending phase at the thoracic and lumbar levels. These speed-dependent changes are clinically critical, influencing movement control and trunk injury risk, especially during descent of forward shoulder elevation. The speed of shoulder movement should be considered during physical examination and intervention.