Measuring Robustness of the Postural Control System to a Mild Impulsive Perturbation

We propose a new metric to assess robustness of the human postural control system to an impulsive perturbation (in this case, a mild backward impulse force at the pelvis). By applying concepts from robust control theory, we use the inverse of the maximum value of the system's sensitivity functi...

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Bibliographic Details
Published in:IEEE transactions on neural systems and rehabilitation engineering 2010-08, Vol.18 (4), p.461-467
Main Authors: Hur, Pilwon, Duiser, Brett A., Salapaka, Srinivasa M., Hsiao-Wecksler, Elizabeth T.
Format: Article
Language:English
Subjects:
Adult
Aged
Aging - physiology
Algorithms
Analysis of Variance
Biomechanical Phenomena
Control system synthesis
Control systems
Data Interpretation, Statistical
Female
Force control
Frequency measurement
Frequency response
Humans
Male
Middle Aged
Models, Biological
Models, Statistical
Older people
Pelvis
Pelvis - physiology
Physical Stimulation
Postural Balance - physiology
Postural control
Posture
Reproducibility of Results
Robust control
Robustness
sensitivity
Spectral analysis
stability
Studies
Young Adult
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Summary:We propose a new metric to assess robustness of the human postural control system to an impulsive perturbation (in this case, a mild backward impulse force at the pelvis). By applying concepts from robust control theory, we use the inverse of the maximum value of the system's sensitivity function ( 1/MaxSens ) as a measure for robustness of the human postural control system, e.g., a highly sensitive system has low robustness to perturbation. The sensitivity function, which in this case is the frequency response function, is obtained directly using spectral analysis of experimental measurements, without need to develop a model of the postural control system. Common measures of robustness, gain and phase margins, however require a model to assess system robustness. To examine the efficacy of this approach, we tested thirty healthy subjects across three age groups: young (YA: 20-30 years), middle-aged (MA: 42-53 years), and older adults (OA: 71-79 years). The OA group was found to have reduced postural stability during quiet stance as detected by center of pressure measures of postural sway. The proposed robustness measure of 1/MaxSens was also found to be significantly smaller for OA than YA or MA ( p =0.001), implying reduced robustness among the older subjects in response to the perturbation. Gain and phase margins failed to detect any age-related differences. In summary, the proposed robustness characterization method is easy to implement, does not require a model for the postural control system, and was better able to detect differences in system robustness than model-based robustness metrics.
ISSN:1534-4320
1558-0210
DOI:10.1109/TNSRE.2010.2052133