Angle Variations in the Wrist and Forearm Joints when Gripping or Rotating a Doorknob

Abstract

We measured the angles of the wrist and forearm joints when gripping or rotating a doorknob using a 3D motion analysis system, and studied the influence of the doorknob gripping position and the torque applied to the rotational axis of the doorknob on these angles. Ten healthy male subjects were asked to grip a doorknob with the elbow flexed at 90° and then rotate the doorknob. There were four conditions (upper, upper right, right, and lower) for the doorknob gripping position and four conditions for the applied torque. Based on the measurement results of the joint angles, we calculated the joint range of motion for the gripping and rotational motions. The analysis of the gripping motion revealed adduction in all gripping positions and extension/pronation in the upper and right positions. The analysis of the rotational motion revealed adduction in the upper and lower positions and extension/pronation in the upper and upper right positions. The analysis of the applied torque showed that, in motions other than pronation and supination, there were changes in the joint range of motion as the applied torque was increased. This is assumed to be due to the movement of the body's center of gravity.