Effect of time window on MVC reference for quantifying spastic cocontraction in spastic paresis

Area of Science:

• Neuroscience
• Biomedical Engineering
• Rehabilitation Science

Background:

• Spastic cocontraction in hemiparesis is typically quantified using electromyographic (EMG) root mean square (RMS) values during maximal voluntary contraction (MVC).
• Existing methods for selecting RMS time windows and applying filters vary significantly, hindering study comparability.
• This variability impacts the reliability of cocontraction indices used in clinical assessments.

Purpose of the Study:

• To evaluate the impact of different RMS window sizes and low-pass filter cutoff frequencies on RMS values during MVC in individuals with chronic hemiparesis.
• To establish standardized parameters for reliable EMG normalization in spastic hemiparesis.

Main Methods:

• Surface EMG was recorded from gastrocnemius and tibialis anterior muscles in 20 participants with hemiparesis and gastrocnemius spasticity.
• RMS values were calculated using sliding windows from 5 to 1,250 ms at various low-pass filter cutoff frequencies (6–100 Hz).

Main Results:

• RMS values stabilized beyond a window size of approximately 168.3 ms, following a first-order model.
• Low-pass filtering below 10 Hz caused a >40% reduction in RMS magnitude, despite maintaining signal shape.

Conclusions:

• Reliable EMG normalization in spastic hemiparesis necessitates a minimum RMS window of ~200 ms during MVC.
• Using unsmoothed EMG is recommended to preserve signal amplitude.
• Standardized methodological parameters will enhance the validity, reproducibility, and comparability of cocontraction indices in research and clinical practice.