1. Introduction
post-stroke, muscle co-contraction, Stroke, stroke, long-term disability
STROKE, DISEASE, STROKE
Persons post-stroke experience excessive muscle co-contraction, and consequently the arm functions are compromised during the activities of daily living. Therefore, identifying instrumental outcome measures able to detect the motor strategy adopted after a stroke is a primary clinical goal. Accordingly, this study aims at verifying whether the surface electromyography (sEMG)-based co-contraction index (Stroke is one of the major causes of long-term disability worldwide, and stroke survivors typically have difficulty performing activities of daily living (ADLs) [Agonist-antagonist muscle co-contraction is an essential and common motor control strategy used by the central nervous system to regulate joint stability and provide movement accuracy [The identification of instrumented outcome measures, able to characterize the neural strategy adopted after a stroke, can be useful in clinical practice for a better understanding of how the disease modifies muscle strategies during the performance of movements, allowing the planning of personalized training [Surface electromyography (sEMG) records the electrical activity of muscles via electrodes placed over the skin, and it is a suitable tool for detecting antagonist muscle co-contraction, allowing to distinguish between physiological and pathological patterns [In fact, for more than five decades, sEMG has been employed in the neurorehabilitation field as a tool to assess muscle activation and improve neuromuscular rehabilitation treatments [However, although the literature has already provided substantial evidence that sEMG applications supply relevant information in the neurorehabilitation area to enhance motor recovery, sEMG-based outcome measures currently have limited use in clinical practice [Appropriate interpretation of sEMG needs both technical and clinical expertise since sEMG parameters extracted from the signal are typically obtained by means of complex methods [The sEMG-based co-contraction index (We have already investigated the changes induced by rehabilitation on the patterns of muscle synergies activation using complex techniques of clustering, which decompose multiple sEMG signals into a limited number of primitive patterns [This study aims at investigating whether an sEMG-based 