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Two functionally different synergies during arm reaching movements involving the trunk
1Department of Exercise Science, Concordia University, Montreal, Quebec, Canada.
Journal of Neurophysiology
|May 1, 1995
Summary
This study reveals how the brain controls reaching movements by coordinating arm and trunk motion. Trunk movements help manage the many degrees of freedom in motor control, ensuring endpoint trajectory remains stable.
Area of Science:
- Neuroscience
- Biomechanics
- Motor Control
Background:
- Motor control systems face the challenge of coordinating redundant degrees of freedom.
- Understanding how trunk movements influence arm reaching is crucial for motor control research.
Purpose of the Study:
- To investigate the influence of voluntary trunk movements on arm endpoint trajectory during reaching tasks.
- To explore the underlying control strategies for redundant motor systems.
Main Methods:
- Subjects performed fast, non-corrected planar arm reaching movements.
- Reaching tasks were combined with voluntary forward or backward trunk motion.
- Analysis focused on endpoint trajectory (direction, error, curvature, velocity) and timing of trunk/arm movements.
Main Results:
- Arm endpoint trajectory characteristics (direction, error, curvature, velocity) were invariant despite trunk movements.
- Trunk motion consistently preceded, overlapped with, and outlasted arm endpoint motion.
- This movement sequence was independent of reaching direction or trunk motion direction.
Conclusions:
- Reaching movements are controlled by two distinct synergies: one for trunk-arm coordination maintaining endpoint stability, and another for interjoint coordination to reach the target.
- The use of functionally specialized synergies offers a solution to the redundancy problem in motor control.