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Computerized Dynamic Posturography for Postural Control Assessment in Patients with Intermittent Claudication
Published on: December 11, 2013
Non-asymptotical postural stabilization strategy during human quiet stance.
Youko Yasutake1, Satoshi Taniguchi, Taishin Nomura
1Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan. youko@bpe.es.osaka-u.ac.jp
Summary
Human quiet stance involves phasic electromyograms (EMGs) from ankle muscles, not just smooth center of mass (CoM) adjustments. This burst-like EMG activity correlates with active ankle torque, suggesting a non-PID control strategy.
Area of Science:
- Biomechanics
- Neuroscience
- Human Motor Control
Background:
- Human quiet stance relies on complex sensorimotor control to maintain balance.
- Previous studies show correlations between ankle muscle electromyograms (EMGs) and center of mass (CoM) movements.
- The precise neural control mechanisms underlying postural sway remain incompletely understood.
Purpose of the Study:
- To investigate the relationship between ankle muscle EMG activity and postural sway dynamics during quiet stance.
- To explore the control strategies employed by the human nervous system for maintaining upright posture.
- To determine if conventional feedback control models can explain observed EMG patterns.
Main Methods:
- Simultaneous measurement of center of pressure, center of mass (CoM), and ankle muscle EMGs during quiet human stance.
- Analysis of EMG activity in relation to CoM kinematics (position, velocity, acceleration).
- Estimation of active ankle torque by modeling ankle joint mechanics and assuming insufficient passive stiffness for stability.
Main Results:
- Ankle extensor EMG activity exhibited phasic, burst-like patterns, contrasting with smooth CoM changes.
- Phasic EMG activity occurred predominantly when CoM acceleration neared zero and terminated when CoM velocity reversed.
- A simulated model using a conventional PID controller failed to replicate the observed phasic EMG.
- A strong correlation was found between estimated active ankle torque and phasic EMG activity.
Conclusions:
- Phasic EMG activity in ankle muscles during quiet stance is a key component of postural control.
- This phasic activity likely generates active ankle torque, contributing to stability.
- Human postural control may employ strategies beyond conventional PID feedback, potentially involving more complex neural computations.
