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Do arm postures vary with the speed of reaching?
K C Nishikawa1, S T Murray, M Flanders
1Department of Biological Sciences, Northern Arizona University, Flagstaff, Arizona 86011, USA.
Journal of Neurophysiology
|May 13, 1999
Summary
Arm posture remains consistent across different reaching speeds in a 3D workspace. This suggests the brain optimizes dynamic forces, not total forces, for efficient arm movement control.
Area of Science:
- Biomechanics
- Motor Control
- Human Movement Science
Background:
- Reaching movements in a single plane show speed invariance.
- The control of complex, multi-joint arm movements remains less understood regarding speed effects.
Purpose of the Study:
- To investigate if arm postures during reaching movements are invariant to speed in a 3D workspace.
- To explore the underlying control strategies for human arm movements.
Main Methods:
- Examined human arm kinematics during reaching tasks with varied initial and final hand positions in 3D space.
- Analyzed arm postures, including the spatial orientation of the arm plane and hand path curvature, across a range of movement speeds.
Main Results:
- Arm kinematics, specifically the arm plane orientation and hand path curvature, showed minimal changes across a wide range of reaching speeds.
- Observed speed-invariant arm postures, contradicting models that optimize total forces (dynamic + quasistatic).
Conclusions:
- Human arm movements exhibit speed-invariant postures in a 3D workspace.
- Findings support a control strategy that optimizes only dynamic forces during reaching, simplifying motor control.
- This suggests a distinct optimization principle for rapid, complex movements.