H reflex Hoffmann (H)-reflex M wave Medicine Neurology & clinical neurophysiology Parkinson's disease activity-based therapy antispasmodic automation biophysics cervical cervical spinal cord cervical spinal cord injury combined intervention corticospinal pathway corticospinal tract electrical stimulation electrically evoked spinal motor potentials electroencephalography electromyography event-related desynchronisation evoked potentials evoked potentials motor functional connectivity gait hand training human intensity effect interlimb coordination locomotion