ORIGINAL RESEARCH article
Front. Neurol.
Sec. Neurorehabilitation
Effect of time window on the MVC reference when quantifying spastic cocontraction in spastic paresis
Maud Pradines 1,2
Jean-Michel Gracies 1,3
Marina Guihard 1
1. UR 7377 BIOTN, Laboratoire Analyse et Restauration du Mouvement, Université Paris Est Créteil (UPEC), France, Créteil, France
2. Service de Rééducation Neurolocomotrice, Hopitaux Universitaires Henri Mondor, Créteil, France
3. Centre Hospitalier de Bastia, Service de Neurorééducation, Universite de Corse Pasquale Paoli, Corte, France
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Abstract
Introduction: In hemiparesis, spastic cocontraction is typically quantified by normalizing electromyographic (EMG) activity to the root mean square (RMS) during maximal voluntary contraction (MVC) of the cocontracting muscle when acting as an agonist. However, the choice of the RMS time window and the use of filtering procedures vary widely across studies, limiting comparability. Here, we evaluated the effect of window size and low-pass filter cutoff frequency (ƒc) on RMS values obtained during MVC in chronic hemiparesis. Methods: Participants with stroke-induced hemiparesis and gastrocnemius spasticity (XV1–GAS–XV3–GAS >5°) were tested in a seated position in the isokinetic ergometer, knee extended and ankle at 90°. Surface EMG was recorded from medial and lateral gastrocnemius, soleus, and tibialis anterior during standardized isometric plantarflexion and dorsiflexion MVCs. RMS values were computed in sliding windows ranging from 5 to 1250 ms (5 ms increments) and analyzed against cutoff frequencies between 6 and 100 Hz. Results: Twenty participants with hemiparesis (age 56.4±7.0 years, time since lesion 7.8±5.7 years) were included. Regardless of muscle, experimental RMS curves as a function of window size followed a first-order model, with high consistency across trials (R² ≈ 0.90, RMSE ≈ 8%). RMS values stabilized beyond 168.3 ms (time constant τ=33.6 ms; 5τ threshold). In contrast, low-pass filtering caused marked amplitude loss, with >40% reduction of RMS magnitude at cutoff frequencies below 10 Hz, despite preservation of signal shape. Discussion: These findings demonstrate that reliable EMG normalization in spastic hemiparesis requires a minimal RMS window of approximately 200 ms during MVC, and that unsmoothed EMG should be used to preserve signal amplitude. Methodological standardization using these parameters can improve the validity, reproducibility, and comparability of cocontraction indices across studies and may facilitate their application to clinical assessments and rehabilitation research in spastic paresis.
Summary
Keywords
Chronic hemiparesis, Electromyography, maximal voluntary contraction, Spastic cocontraction, Window width
Received
29 September 2025
Accepted
30 January 2026
Copyright
© 2026 Pradines, Gracies and Guihard. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Maud Pradines
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