J Neurophysiol (November 1, 2002). 10.1152/jn.00946.2001
Submitted on 16 November 2001
Accepted on 9 July 2002

Circle-Drawing Movements at Different Speeds: Role of Inertial Anisotropy

 ¹School of Kinesiology (MC 194) and  ²Department of Psychology, University of Illinois at Chicago, 60608;  ³Department of Physical Therapy (MC 898), University of Illinois at Chicago, 60612;  ⁴Department of Neurological Sciences, Rush Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612; and  ⁵Department of Epidemiology and Biostatistics, Norman J. Arnold School of Public Health, University of South Carolina, Columbia, South Carolina 29208

Pfann, Kerstin D., Daniel M. Corcos, Charity G. Moore, and Ziaul Hasan. Circle-Drawing Movements at Different Speeds: Role of Inertial Anisotropy. J. Neurophysiol. 88: 2399-2407, 2002. This study investigated the role of inertial anisotropy at the hand in causing distortions in movement. Subjects drew circles in the horizontal plane at four locations in the workspace at three instructed paces using elbow and shoulder movements. Specifically, we tested two hypotheses, which we would expect if the anisotropy of inertia were not completely accounted for by the CNS when generating circle-drawing movements: 1) speed will affect the circularity of figures, with faster movements associated with greater elongation into an oval shape, irrespective of workspace location for configurations with a similar angle between the forearm and upper arm. 2) The elongation of the circle at fast speeds will be in the direction of least inertia. The results showed that despite individual differences in the speed dependence of the relative motions at the elbow and the shoulder, the circularity decreased (distortion increased) with increased speed, and workspace location had no effect on circularity. We also found that the elongation of the circles at fast speeds was in a direction close to but significantly different from the direction of least inertia for three workspace locations and was in the direction of least inertia for the fourth location. We suggest that the elongation results from lack of full accounting by the CNS of the anisotropy of viscosity and inertia.