Neuromotor Changes After a Cervical Spinal Cord Injury: Bilateral Assessment of Unilateral Tasks

Cervical spinal cord injuries (cSCI) severely affect upper limb function, yet research on post-injury neuromotor abilities is limited. In response, we developed an assessment integrating clinical, kinematic and muscle activity measures. Twelve cSCI (C5-C7) and six unimpaired participants underwent a clinical (Range Of Motion and Manual Muscle tests) and an instrumented assessment. During the latter, bilateral upper body kinematics and muscle activity were recorded as participants performed a set of unilateral movements, i.e. reaching movements toward different heights-directions and an object transfer along an arch-shaped structure (arc task). Kinematics and neuromuscular indicators were analyzed following a two-tiered approach: comparing unimpaired and cSCI and differentiating more and less impaired arms within the cSCI cohort based on their ability to complete the arc task. Clinical tests revealed shoulder mobility and strength limitations in cSCI participants, with a significant weakness in elbow extension noted in more impaired arms. The instrumented assessment revealed reduced movement speed, smoothness and accuracy in the cSCI cohort, primarily due to weaknesses in the pectoralis muscle affecting contralateral movements and deltoids affecting ipsilateral movements. Muscle activations were detected in the non-moving arm of cSCI participants, particularly noticeable during movements toward greater heights or in a contralateral direction. The pronounced weakness in the pectoralis muscle of the more impaired cSCI arms explained the related ability to complete only 28% of the arc task. Our findings provide a thorough insight into changes in upper limb neuromotor function following cSCI, underscoring motor deficits and related alterations in bilateral muscle activity.