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3-D trajectory of body sway angles: A technique for quantifying postural stability

Hejda J., Cakrt O., Socha V., Schlenker J., Kutilek P.

Biocybernetics and Biomedical Engineering

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2015

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Vol. 35, no. 3

185--191

EN

The article focuses on a non-invasive method of quantifying human postural stability. Recent alternatives to quantify human postural stability have several limitations – the major one being the evaluation of only two physical quantities of body movement in 3D space – however, a complex movement pattern can be described better using three physical quantities. A cheap 3DOF orientation tracker (Xsens MTx unit) placed on patient's trunk was used to measure roll, pitch and yaw. Using a novel method based on the total length of the 3-D trajectory of body sway angles, we are able to evaluate 3-D movements of the trunk. The trajectory length obtained by plotting roll, yaw and pitch vs. each other (i.e. curve in the 3-D plot) was used to identify a pathological balance control. In this study, ten patients with progressive cerebellar ataxia and eleven healthy subjects were measured and a statistical analysis was performed. The results yielded by new method show that the total trajectory lengths of patients with cerebellar disease are significantly larger than the total trajectory lengths of healthy subjects. It is evident from the median of the total trajectory lengths that the method based on the data obtained by an inexpensive orientation tracker may be used to quantify human postural stability and enables for studying body sway in 3-D space. For example, the 3-D deviations of the trunk angles in a time period that are caused by a tremor in 3-dimensional space can be studied accordingly by the method.

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Quantification of gait asymmetry in patients with ankle foot orthoses based on hip–hip cyclograms

Kutilek P., Socha V., Viteckova S., Svoboda Z.

Biocybernetics and Biomedical Engineering

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2014

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Vol. 34, no. 1

46--52

EN

Our work focuses on a new approach of studying asymmetry in walking based on the orientation of the synchronized bilateral hip–hip cyclograms. Patients with foot drop were included in the study and were asked to walk without an orthosis, and with foot-up splint, calf mounted support strap and ankle wrap. The hip–hip cyclograms were created to quantify gait asymmetry before and immediately after the application of ankle foot orthoses. This approach has never been applied before to study the gait asymmetry in patients with ankle foot orthoses. In order to quantify the gait asymmetry, we have tested the application of the approach based on the inclination angle of the synchronized hip–hip cyclograms. The symmetry index was used as a comparative method to evaluate the symmetry of bipedal walking. The results indicate the correlation between the symmetry index and inclination angle of the synchronized hip–hip cyclograms. The methods based on the inclination angle and symmetry index show slightly different results because the symmetry index depends on discrete variables and is unable to reflect the asymmetry as it evolves over a complete gait cycle. The inclination angle of the hip–hip cyclogram depends on the complete gait cycle. Except for the inclination angles of patients with the support strap, the results show that the new approach did not identify significant improvement in the gait symmetry after the application of the orthoses. The approach based on the orientation of the hip–hip cyclograms can be used as an additional approach for determining the gait asymmetry.

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Differences in evaluation methods of trunk sway using different MoCap systems

Kutilek P., Socha V., Cakrt O., Svoboda Z.

Acta of Bioengineering and Biomechanics

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2014

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Vol. 16, no. 2

85--94

EN

The position of the trunk can be negatively influenced by many diseases. Several methods can be used for identifying defects in balance and coordination as a result of pathology of the musculoskeletal or nervous system. The aim of this article is to examine the relationship between the three methods used for analysis of trunk sway and compare two fundamentally different MoCap systems. We used a camera system and a 3DOF orientation tracker placed on subject’s trunk, and measured inclination (roll) and flexion (pitch) during quiet stance. Ten healthy participants in the study were measured with eyes open and closed. The pitch versus roll plots of trunk were formed, and the area of the convex hull, area of confidence ellipse and total length of the trajectory of the pitch versus roll plot were calculated. The statistical analysis was performed and strong correlation between the area of the convex hull and area of the confidence ellipse was found. Also, the results show moderate correlation between the area of the confidence ellipse and total length of the trace, and moderate correlation between the area of the convex hull and total length of the trace. In general, the different MoCap systems show different areas and lengths but lead to the same conclusions. Statistical analysis of the participants with eyes open and eye closed did not show significant difference in the areas and total lengths of the pitch versus roll plots.