text: This parameter is often used in biomechanics, when describing the motion of joints of the body. For any period of time, joint motion can be seen as the movement of a single point on one articulating surface with respect to the adjacent surface (usually distal with respect to proximal). The total translation and rotations along the path of motion can be defined as the time integrals of the instantaneous translation and rotation velocities at the IHA for a given reference time.
  In any single plane, the path formed by the locations of the moving instantaneous axis of rotation (IAR) is known as the centroid, and is used in the description of joint motion.