Reduced reciprocal inhibition during clinical tests of spasticity is associated with impaired reactive standing balance control in children with cerebral palsy.

It has been hard to relate alterations in muscle coordination during functional movements to alterations in the muscle's response to isolated joint rotations as applied during (clinical) assessments of hyper-reflexia. Here, we performed a more comprehensive assessment of the altered muscle response to isolated joint rotations in children with cerebral palsy (CP) by not only considering muscle activity in response to stretch but also agonist-antagonist co-activation. Muscle co-activation in response to isolated joint rotations in relaxed patients has been attributed to reduced reciprocal inhibition in the spinal cord. We found that muscle co-activation during isolated joint rotations was correlated to muscle co-activation during perturbed standing, an important functional movement. Therefore, increased muscle co-activation during standing balance control might - at least partially - result from reduced reciprocal inhibition in the spinal cord. In contrast, we found very few relations between the mean muscle activity during isolated joint rotations and perturbed standing. This might be due to the sensitivity of the response to stretch to stretch velocity, posture, and baseline muscle activity, all of which largely differed between the two conditions. Our results indicate that clinical assessment of reduced reciprocal inhibition during isolated joint rotations might provide information about balance impairments.