An increase in the aging population around the world and in degenerative diseases has caused an epidemic of stroke. Hence, rehab equipment for treating its after-effects has been actively developed. A repeated upper-body rehab exercise is required and this exercise can only yield good results when its accurate motion is guided by a therapist. However, few kinematics studies have been conducted based on design variables such as changes in the rotational central axis and body measurement. So, this study analyzed the angular changes in two motions of the elbow (Flexion-Extension: F-E, Pronation-Supination: P-S) and three motions of the scapula (Anterior-Posterior tilt: A-P, Internal-External rotation: I-E, Upward-Downward rotation: U-D) based on changes in the arm support length and central axis location.
Eight healthy subjects participated in this study. Rehabilitation equipment for the upper limb, which can be adjusted to different arm support lengths and central axis locations, was used as the experimental equipment. The length could be adjusted to five levels (280 mm, 220 mm, 160 mm, 100 mm, and 40 mm). In the case of an experiment involving changes in the axis locations, the length was fixed as 280 mm, which allowed five different axis locations. Each subject implemented a rotational movement passively at an angular velocity of 30°/s.
In this study, we observed changes in the motion patterns of the upper-limb rotational movement based on the length and the location. The patterns based on the two design variables revealed a consistent tendency under the elbow (forearm) and the scapula (shoulder rhythm). Yet, three scapula motions showed little changes in the angular width, and only I-E showed an angular width of 5°. First, with respect to the tendency of the five motions based on changes in the 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 (Location 1 → Location 5) confirmed a decreased angular width owing to a relatively small rotational movement at Location 5.
The F-E motion of the elbow clearly showed two time cycles per rotation. Other motions revealed one time cycle per rotation. With respect to the upper-body rotational movement, we confirmed that motions related to the forearm were more active than motions related to the shoulder.
