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Measuring movement irregularity in the upper motor neurone syndrome using normalised average rectified jerk
J Alastair Cozens1, Bipin B Bhakta
1Department of Rehabilitation Medicine, Grampian University Hospitals Trust, Woodend Hospital, Eday Road, AB15 6LS, Aberdeen, UK. Alistair.Cozens@arh.grapian.scot.nhs.uk
Summary
A new method, normalized average rectified jerk (NARJ), accurately measures upper motor neurone (UMN) syndrome movement irregularity, overcoming limitations of previous methods dependent on movement duration.
Area of Science:
- Biomedical Engineering
- Neuroscience
- Rehabilitation Science
Background:
- Movement irregularity is a key but challenging-to-quantify feature of upper motor neurone (UMN) syndrome.
- Existing measures like Average Rectified Jerk (ARJ) are duration-dependent, limiting their accuracy in UMN patients with slower movements.
Purpose of the Study:
- To validate a novel duration-independent measure, normalized average rectified jerk (NARJ), for quantifying movement irregularity in UMN syndrome.
- To compare the effectiveness of NARJ against ARJ in distinguishing movement patterns across different subject groups.
Main Methods:
- Elbow flexion/extension movements were recorded using electro-goniometers and accelerometers in 9 control subjects and 18 hemiparetic stroke patients.
- NARJ was calculated using a proposed normalization technique and compared with ARJ across varying movement durations, including artificially generated trajectories.
- Criterion validity was assessed via correlation with expert subjective ratings, and construct validity by discriminating between control and patient groups.
Main Results:
- NARJ demonstrated minimal variation (2.6%) with a two-fold difference in movement duration, compared to ARJ's significant change (706%).
- NARJ showed strong criterion validity (Spearman correlation 0.92, p<0.01) with expert ratings of irregularity.
- NARJ significantly differentiated movements in right hemiparetic patients from controls (p<0.02), unlike ARJ.
Conclusions:
- Normalized average rectified jerk (NARJ) is a valid and reliable measure of movement irregularity in the upper motor neurone (UMN) syndrome.
- NARJ overcomes the duration-dependence limitations of ARJ, offering improved accuracy for assessing motor control deficits in neurological conditions.