Analysis of Muscle Activation in the Lower Limbs During Walking in Individuals With Stroke Sequelae

Stroke is the leading cause of acquired disability in France and the third leading cause worldwide. The number of new cases will continue to rise in the coming years, reaching 23 million worldwide by 2030 (Boursin et al., 2018; GBD 2019 Stroke Collaborators, 2021). Following a stroke, nearly 9 out of 10 people experience impaired motor function and 65% of individuals experience impaired walking activity. The loss or impairment of walking is a significant factor in limiting social participation and quality of life (Daviet et al., 2022; Lord et al., 2004; Mayo et al., 2002).

Muscle activation abnormalities are common after a stroke, particularly muscle coactivation (MCo) abnormalities, defined as the simultaneous activity of an agonist muscle and an antagonist muscle around the same joint. MCo is used to assess agonist/antagonist muscle synergy (Rosa et al., 2014). This parameter measures the ability of the agonist/antagonist pair to stabilize support during walking, as well as the ability to relax muscles to clear the step during the swing phase (Busse et al., 2005; Falconer & Winter, 1985; Latash, 2018). In the literature, two measures of MCo are mainly used with surface electromyography (sEMG): a temporal measure, called coactivation duration (CoD), defined as the duration during which the agonist/antagonist muscle pair is active simultaneously, and an intensity measure, called coactivation index (CoI), defined as the ratio of the antagonist muscle activation amplitude to the agonist muscle activation amplitude or the agonist/antagonist pair (Rosa et al., 2014). The literature has highlighted abnormal levels of MCo in post-stroke individuals compared to healthy subjects, both at the ankle and knee, but also regardless of the phase of the gait cycle (Kitatani et al., 2016; Rosa et al., 2014). Current research reports that abnormal levels of MCo (CoD or CoI) appear to be associated with a deterioration in walking speed, a determining factor in walking ability and mobility in society (Chow et al., 2012; Kitatani et al., 2016; Rinaldi et al., 2017). These findings reinforce the importance of measuring MCo in routine practice. These findings reinforce the importance of measuring MCo in clinical practice. However, the literature reports wide variability in MCo values, even among participants with similar profiles in terms of motor impairment and walking ability (Banks et al., 2017; Mizuta et al., 2024). For example, in the study by Lamontagne et al. (2000), post-stroke individuals had low MCo values for a moderate level of impairment, while Kitatani et al. reported high MCo values for a post-stroke population with the same level of motor impairment. However, these compared groups show significant variability in parameters, both in terms of population characteristics and MCo methodological assessment parameters, thus requiring individual rather than collective analysis. It is important to identify anomalies in muscle activation, particularly MCo, in order to improve our understanding of the mechanisms involved in gait recovery. A better understanding will enable the development of more effective interventions for individuals with stroke sequelae.