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Ankle muscle stiffness alone cannot stabilize balance during quiet standing
Pietro G Morasso1, Vittorio Sanguineti
1Department of Informatics, Systems, Telecommunication, University of Genova, I-16145 Genova, Italy. morasso@dist.unige.it
Journal of Neurophysiology
|October 5, 2002
Summary
Ankle muscle stiffness alone cannot maintain balance during quiet standing. New simulations show that active control is necessary to prevent mechanical instability and maintain posture.
Area of Science:
- Biomechanics
- Neuroscience
- Human motor control
Background:
- The hypothesis that ankle muscle stiffness alone stabilizes balance during quiet standing is re-examined.
- Previous methods for estimating ankle stiffness from posturography are questioned due to ignoring motoneuronal activity.
Purpose of the Study:
- To evaluate the accuracy of a new method for estimating ankle stiffness.
- To investigate the role of anticipatory active control in maintaining postural stability.
- To simulate the mechanical stability of the ankle-muscle system.
Main Methods:
- Analysis of posturographic data to estimate ankle stiffness.
- Development and simulation of a realistic musculoskeletal model of the ankle.
- Investigation of system dynamics under conditions with and without anticipatory control.
Main Results:
- The recently proposed method for estimating ankle stiffness from posturography is demonstrated to be inaccurate.
- Simulations reveal mechanical instability in the absence of anticipatory active control.
- Active stiffness mechanisms contribute significantly to the restoring forces required for balance.
Conclusions:
- Anticipatory active control is crucial for maintaining balance during quiet standing.
- The direct estimation of ankle stiffness from posturography is unreliable.
- Muscles actively contribute to postural stability through stiffness modulation.