Methods for assessing coactivation in the lower limb muscles during overground walking poststroke: a systematic review

Recovering an independent and efficient gait is essential for social participation and quality of life after a stroke. However, muscle coactivation (MCo) is considered a major limiting factor. This study aimed to systematically review the methods used to assess lower limb MCo during overground walking in stroke survivors. Major scientific databases were searched, and 19 articles were ultimately included. Data extraction focused on gait cycle detection, surface electromyograph (sEMG) acquisition settings, signal processing, and MCo calculation, specifically the coactivation index (CoI) and coactivation duration (CoD). Results revealed variability in methodological choices across all stages required to assess MCo. Regarding acquisition and processing approaches, several commonalities were identified, such as the use of Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles guidelines for electrode placement and the application of a single threshold for muscle activation detection. Conversely, significant variability was found in the selection of gait cycle phases and signal filtering techniques. Furthermore, this heterogeneity was particularly pronounced in the final MCo calculation stage. Specifically, CoI represents the most diverse approach, with seven distinct formulas, which prevents the proposal of a common method. Conversely, CoD measurement shared a unique calculation formula associated with more common methodological elements, allowing for the proposal of a standardized approach. This common method was also aligned with current sEMG recommendations. Overall, although standardized methods have been established to assess the MCo, neither CoI nor CoD has yet undergone sufficient reliability testing to support routine clinical use. This review underscores the need for methodological rigour to improve the comparability of MCo assessments in stroke rehabilitation research.