Abstract
[Purpose] The aim of this study was to clarify the influence of trunk rotation and side bending, as well as abduction of the scapula in the scapulothoracic joint, on unilateral and bilateral functional reach (FR) tests; and to elucidate the relationship between reach distance and center of pressure (COP) trajectory in front-back and right-left excursion. [Participants and Methods] The subjects were 21 healthy adult males and females, who performed two types of reach tasks, a typical FR and a bilateral FR with restricted trunk movement. We measured the maximum reach distance, trunk rotation and side bending, scapula abduction distance, and COP trajectory at maximum reach. Each of the variables were compared and their correlations verified. [Results] In a comparison of the two tasks, we found significant differences in the following 4 items: reach distance, right-left x-axis COP trajectory length, degree of trunk rotation, and scapular abduction distance. Significant differences were not observed in the front-back y-axis COP trajectory length and degree of trunk lateral flexion. Trunk rotation led to scapular abduction in FR; the scapula appears to rotate upward in bilateral FR. The degree of correlation between the y-axis COP trajectory length and reach distance was similar in both measurements, and a negative correlation was found between trunk rotation and lateral flexion in FR. [Conclusion] The movement factors in FR involve trunk rotation, abduction of the scapula in the scapulothoracic joint, and lateral movement of the COP on the side of the arm measured. On the other hand, for movement factors in bilateral FR, trunk rotation and lateral flexion, as well as lateral movement of the COP, were minimal. Thus, the scapula appears to rotate upward. The results of this study imply that unilateral and bilateral FR reach tests are dynamic balance tests that exert posture control, including the aforementioned movement strategies, and reflect equivalent stability limits.
