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Directional effects of changes in muscle torques on initial path during simulated reaching movements
G F Koshland1, B Marasli, A Arabyan
1Department of Physiology, Arizona Health Sciences Center, University of Arizona, Tucson, AZ 85724, USA, Koshland@u.arizona.edu
Experimental Brain Research
|September 29, 1999
Summary
Understanding how the nervous system controls arm movements is key. Scaling muscle torque at shoulder and elbow joints uniformly adjusts hand speed, but path direction control is complex and varies across the workspace.
Area of Science:
- Neuroscience
- Biomechanics
- Motor Control
Background:
- Adults exhibit accurate and controlled reaching movements.
- The neural control strategies for generating muscle activity during arm movements remain incompletely understood.
- The impact of muscle torque variations on the kinematics of complex arm movements is largely unknown.
Purpose of the Study:
- To investigate the sensitivity of initial hand path kinematics to changes in muscle torque during arm movements.
- To characterize how variations in torque amplitude and timing at shoulder and elbow joints influence movement direction and speed.
Main Methods:
- Utilized computer simulations to model arm movements in the horizontal plane.
- Systematically manipulated torque amplitude and timing at single and multiple joints.
- Simulated movements towards 12 different directions.
Main Results:
- Simultaneous scaling of torque amplitude at the shoulder and elbow joints uniformly affected initial hand speed across all movement directions.
- Changes in torque amplitude or timing at single or multiple joints had non-uniform effects on initial hand path direction.
- The sensitivity of initial path direction to torque variations differed across the workspace.
Conclusions:
- Scaling torque amplitude at both shoulder and elbow joints is a simple strategy for controlling movement speed regardless of direction.
- Achieving a specific initial path direction requires different torque adjustments depending on the arm's position in the workspace.
- The variability in torque solutions suggests that the motor system may employ different strategies for accurate path control in different workspace regions.