Examination of body static rotation related to step length asymmetry: biomechanics of the thorax and pelvis

[Purpose] This study determined whether the results of the mobility assessment of pelvic and thoracic rotation (static evaluation), which is often used in clinical settings, are related to step length asymmetry. Moreover, we identified the postural evaluation of rotation that may be related to gait asymmetry. [Participants and Methods] We hypothesize that a certain relationship exists between the static assessments of pelvic rotation and step length asymmetry. Fifteen healthy adult males participated in static posture and gait motion analyses using a motion-capture system. The static evaluation was analyzed using three parameters: pelvic rotation in standing, pelvic rotation with kneeling, and thorax rotation in sitting. [Results] The relationship between the asymmetric variables obtained from static evaluation and gait observations demonstrated a significant correlation. The asymmetric variables of step length and asymmetric variables of thorax rotation in sitting showed a significant relationship. Furthermore, significant correlations were found between asymmetric variables of pelvic rotation during gait and asymmetric variables of step length and between asymmetric variables of pelvic rotation during gait and asymmetric variables of thorax rotation in sitting. [Conclusion] This study revealed asymmetric relationships between thorax rotation in sitting test and step length asymmetry in the gait. Asymmetry in the thorax rotation in sitting may be caused by a gait with biased pelvic rotation.