Directional control of planar human arm movement.
Gerald L. Gottlieb, Qilai Song, Gil L. Almeida , Di-an Hong,
and Daniel Corcos.
Boston University - NeuroMuscular Research Center, 44 Cummington St.
Boston, Massachussetts 02215, Universidade Estadual de Campinas, Campinas, Sao
Paulo, Brazil 13100, Corporate Manufacturing Research Center, Motorola, Inc.
Schaumburg, IL 60196, School of Kinesiology (M/C 194), University of Illinois
at Chicago, Chicago, Illinois 60680, Department of Neurological Sciences Rush
Medical College, Chicago, Illinois 60612.
APStracts 4:215N, 1997.
ABSTRACT
We examined the patterns of joint kinematics and torques in two kinds of
sagittal plane reaching movements. One consisted of movements from a one fixed
initial position with the arm partially outstretched, to different targets,
equidistant from the initial position and located according to the hours of a
clock. The other series added movements from different initial positions and
directions and over 40-80 cm distances. Dynamic muscle torque was calculated
by inverse dynamic equations with the gravitational components removed. In
making movements in almost every direction, the dynamic components of the
muscle torques at both the elbow and shoulder were almost linearly related to
each other. Both were similarly shaped, biphasic, almost synchronous and
symmetrical pulses. These findings are consistent with our previously reported
observations that we termed a linear synergy.
The relative scaling of the two joint torques changes continuously and
regularly with movement direction. This was confirmed by calculating a vector
defined by the dynamic components of the shoulder and elbow torques. The
vector rotates smoothly about an ellipse in intrinsic, joint torque space as
the direction of hand motion rotates about a circle in extrinsic Cartesian
space. This confirms a second implication of linear synergy that the scaling
constant between the linearly related joint torques is directionally
dependent.
Received 31 July 1996; accepted in final form 25 August 1997.
APS Manuscript Number J608-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 5 September 1997