Neuromuscular constraints on muscle coordination during overground walking in persons with chronic incomplete spinal cord injury

• Persons with chronic incomplete spinal cord injury (iSCI) exhibit significant reduced muscle coordination during overground walking as compared to age-matched adults.
• Neuromuscular constraints following iSCI contribute to person-specific deficits in overground walking.
• Neuromuscular mechanisms underlying gait deficits may provide guidance for targeted SCI rehabilitation.

ObjectiveIncomplete spinal cord injury (iSCI) disrupts motor control and limits the ability to coordinate muscles for overground walking. Inappropriate muscle activity has been proposed as a source of clinically observed walking deficits after iSCI. We hypothesized that persons with iSCI exhibit lower locomotor complexity compared to able-body (AB) controls as reflected by fewer motor modules, as well as, altered module composition and activation.MethodsEight persons with iSCI and eight age-matched AB controls walked overground at prescribed cadences. Electromyograms of fourteen single leg muscles were recorded. Non-negative matrix factorization was used to identify the composition and activation of motor modules, which represent groups of consistently co-activated muscles that accounted for 90% of variability in muscle activity.ResultsMotor module number, composition, and activation were significantly altered in persons with iSCI as compared to AB controls during overground walking at self-selected cadences. However, there was no significant difference in module number between persons with iSCI and AB controls when cadence and assistive device were matched.ConclusionsMuscle coordination during overground walking is impaired after chronic iSCI.SignificanceOur results are indicative of neuromuscular constraints on muscle coordination after iSCI. Altered muscle coordination contributes to person-specific gait deficits during overground walking.