Increased antagonist muscle activity in cervical SCI patients suggests altered reciprocal inhibition during elbow contractions

- Influence of SCI on muscle activations was investigated during actual contractions.
- Antagonist muscles of SCI participants were more activated than those of controls.
- Reciprocal facilitation may lead to increased activation of antagonist muscles.

ObjectiveAfter spinal cord injury (SCI), the antagonist muscles activation is increased during voluntary contractions and reflex conditioning protocols. This increase can be the result of both muscle atrophy and reciprocal facilitation mechanism. It remains however unclear to what extent increased antagonist muscles activation could be rather attributable to central vs. peripheral changes during voluntary contractions achieved by SCI participants.MethodsWe investigated the activations of elbow extensors and flexors during isometric elbow flexion and extension contractions performed at 3 force levels by 10 healthy participants and 8 participants with cervical SCI (cSCI).ResultsAt similar force level and absolute net torque in flexion, the antagonist muscles activation was increased for the participants with cSCI. At similar absolute net torque in extension, the activations of agonist and antagonist muscles were increased for the participants with cSCI.ConclusionDuring flexion contractions, increased antagonist muscles activation may be explained by extensors atrophy or reciprocal facilitation. During extension contractions, increased antagonist muscles activation may reflect the importance of reciprocal facilitation as antagonist muscles were evaluated as intact by clinical testing and maximal net joint torque recording.SignificanceThese results in cSCI participants revealed an increased activation of antagonist muscles, which may reflect a reorganization of the spinal reflexes and their supraspinal control involved during isometric elbow contractions.