Abstract
The isolated paralysis of the dorsal erector trunci in the angular point of the convex curve of a juvenile scoliosis in progress by resecting the corresponding rami dorsales of the spinal nerves gave the opportunity to analyse electromyographically with electrodes on the skin before and after the operation in the two basic positions: standing comfortably upright and bending the trunc with extended arms. Thus the electric activity of the erector trunci could be isolated from the total activity of all the measured dorsal muscles. The pre-operative hyperactivity of the erector trunci on the convex side in the protogenic curve increases unproportionally strongly when the trunk is bent, trunk bending regarded as an example for a symmetric exertion. This pre-operative hyperactivity is eliminated by the operation which denervates the erector trunci.