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Moving effortlessly in three dimensions: does Donders' law apply to arm movement?
J F Soechting1, C A Buneo, U Herrmann
1Department of Physiology, University of Minnesota, Minneapolis 55455, USA.
Summary
Donders' law predicts a unique arm posture for each hand location. However, experiments show arm posture depends on the movement
Area of Science:
- Biomechanics
- Motor Control
- Human Movement Science
Background:
- Donders' law posits a unique arm posture for every hand location in space.
- This principle is fundamental in understanding human arm movement control.
Purpose of the Study:
- To experimentally test Donders' law for arm posture.
- To investigate factors influencing arm posture variations during pointing movements.
Main Methods:
- Human subjects performed pointing movements to target locations from various initial hand positions.
- Arm posture (shoulder and elbow angles) was recorded using video cameras at movement start and end.
Main Results:
- Arm posture at a given hand location varied depending on the initial movement starting point.
- Donders' law was violated under these experimental conditions.
- Final arm posture could not be predicted from initial kinematics alone.
Conclusions:
- Arm posture during reaching movements is not solely determined by the target hand location.
- Minimization of work required for arm transport successfully predicted final arm postures.
- Motor control strategies may involve optimizing energy expenditure during reaching.