Lower limb medical exoskeleton are designed to assist patients during walking and are of particular interest in the case of cerebro-muscular conditions such as cerebral palsy, spinal cord injuries or stroke recovery. In those cases, the spasticity could limit the patient possibilities. Rehabilitation techniques should those patients in their regulation of muscle contractions without sacrificing their capabilities. This contribution introduces a new method for exoskeleton control based on a detailed bio-kinematic analysis. Existing approaches rely on  neuro-fuzzy methods that could not correctly capture the patient's movements. The neuro-motor index is dedicated to patient with cerebral palsy or stroke recovery conditions and is compatible with online processing, as required for exoskeleton control.