Abstract
An analysis was conducted of the movement that takes place in the glenohumeral joint while a subject performs shoulder flexion/extension on the Cybex isokinetic dynamometer (CYBEX, Ronkonkoma, NY). The initial position of the glenohumeral joint was extrapolated from bony landmarks. Light-emitting diodes associated with the Watsmart three-dimensional optoelectronic motion analysis system were placed on the subject's arm and traced while he worked on the Cybex. Nine subjects took part in the experiment, and pooling their data showed that on average the joint elevated 8 cm. This constitutes 12.5% of the distance from the glenohumeral joint to the wrist. A combination of elbow flexion and protraction/distraction of the shoulder complex compensated for glenohumeral joint movement. Because the perpendicular distance from the shoulder to the handle of the Cybex has been reduced by 12.5%, so should the value recorded by the Cybex data reduction computer.