Influence of thoracic asymmetry on trunk movement patterns during sit-to-stand motion.

[Purpose] To investigate the relationship between thoracic asymmetry in the seated position, sagittal head position, and trunk movement patterns during the sit-to-stand motion. [Participants and Methods] Twenty-three healthy adults participated. Using a three-dimensional motion analysis system, we calculated the anteroposterior diameter ratios (right/left) of the upper and lower thorax at rest and measured the sagittal displacement of the head relative to the thorax. During the sit-to-stand task, we analyzed trunk movement relative to the pelvis and hip joint flexion-extension angles. [Results] Of the 23 participants, 20 exhibited leftward thoracic deviation relative to the pelvis. In these cases, trunk flexion preceded hip flexion, reaching maximum flexion before the hip joint. Significant leftward trunk rotation also occurred during the transition from flexion to extension, compared with that in the initial position. A correlation was observed between upper thoracic asymmetry and trunk flexion and between forward head displacement and trunk flexion. [Conclusion] Thoracic asymmetry and sagittal head position were associated with trunk movement patterns during sit-to-stand. These factors may be important considerations for physical therapy interventions aimed at improving sit-to-stand performance.