Muscle Synergies: Implications for Clinical Evaluation and Rehabilitation of Movement

Abstract

We present a method called muscle synergy analysis, which can offer clinicians insight into both underlying neural strategies for movement and functional outcomes of muscle activity. Although neural dysfunction is central to many motor deficits, neural activity during movements is not directly measurable. Consequently, the majority of clinical tests focus on evaluating motor outputs at the behavioral and kinematic levels. However, altered behavioral or kinematic outcomes could be the result of multiple distinct neural abnormalities with very different muscle coordination patterns. Because muscle activity reflects motoneuron activity and generates the forces that produce behavioral outcomes, an analysis of muscle activity may provide a better understanding of the functional neural deficits in the impaired nervous system. Unfortunately electromyographic datasets can be large, highly variable, and difficult to interpret, precluding their clinical utility. Computational analyses can be used to extract muscle synergies from such datasets, revealing underlying patterns that may reflect different levels of neural function. These muscle synergies are hypothesized to represent motor modules recruited by the nervous system to flexibly perform biomechanical subtasks necessary for movement. For example, hemiparetic stroke patients exhibit differences in the number of muscle synergies, which may reflect disruptions in descending neural pathways and are correlated to deficits in motor function. Muscle synergy analysis may thus offer the clinician a better view of the neural structure underlying motor behaviors and how they change in motor deficits and rehabilitation. Such information could inform diagnostic tools and evidence-based interventions specifically targeted to a patient’s deficits.

Modular control of varied locomotor tasks in children with incomplete spinal cord injuries

“…Identification of fewer modules required to account for the muscle activation across locomotor tasks in children with ISCIs provides evidence of the effect of ISCI on neuromuscular control mechanisms (Safavynia et al 2011). Identifying underlying mechanisms associated with locomotor control is critical for the development of rehabilitation interventions designed to restore walking and locomotor function after pediatric-onset ISCI.…”

“…Examination of modular control not only provides insight into the mechanisms underlying locomotor control but also provides information regarding the effects of neurological injuries (Cheung et al 2012;Safavynia et al 2011). For example, adults poststroke exhibit fewer modules during walking, and this constraint on modular output is associated with decreased gait speed (Bowden et al 2010;Clark et al 2010) and poor biomechanical control .…”

Extracting and study of synchronous muscle synergies during fast arm reaching movements

“…Our results for activation or inactivation of muscles in the synergies were matched to our previous expectations due to physiological knowledge. Muscle synergies are applicable for clinical evaluation and rehabilitation of movements [21].…”

Can robotic-based top-down rehabilitation therapies improve motor control in children with cerebral palsy? A perspective on the CPWalker project

“…In this sense, the concept of muscle synergy has emerged in neuroscience and has been proposed as a mechanism for neural control of normal movement [9]. Muscle synergies in healthy subjects represent functional muscle coordination patterns used to reliably produce motor functions during natural motor behaviors (4-5 synergies for gait) [7,9,10]. Interestingly, a reduced number of synergies during gait have been reported for children with CP (2-3 synergies).…”