Kinematic analysis based on changes in arm support length and central axis location through rotational motion of the upper limb

An upper-body rehabilitation exercise can only yield good results when its accurate motion is guided by therapists. However, few kinematics studies have been conducted based on design variables, such as changes in the rotational central axis and body measurement. The aim of this study is to analyze the angular changes in two motions of the elbow and shoulder rhythm, based on changes in the arm support length and central axis location. Eight healthy subjects participated in this study. The arm support length and central axis location in the experimental rehabilitation equipment could be adjusted to five levels. Each subject passively implemented a rotational movement, at an angular velocity of 30°/s. First, with respect to the tendency of the five motions based on changes in lengths, the prolonged length showed a decreased angular width. Second, in terms of the tendency of the five motions based on changes in the locations, a relatively long distance between the handle and the axis confirmed a decreased angular width, owing to a relatively small rotational movement at Location 5. We observed significant changes in the motion patterns of the upper-limb rotational movement, based on the length and location.