The H Reflex in Normal, Spastic, and Rigid Subjects: Studies

Under appropriate conditions, a single shock to the human tibial nerve will evoke two discrete action potentials in the calf muscles. The first potential, the M wave, results from direct stimulation of motor nerve fibers. The second potential, the H wave, is the expression of a monosynaptic reflex, which runs in afferents from the muscle and back again through efferents of the same muscle. 11,13 Since no internuncial neurons are involved, the size of the second action potential will provide a measure of motoneuron excitability under a variety of experimental and pathological conditions. 2 The H reflex has been widely used in the study of human physiology, both normal 3,6,11,13,18,19 and abnormal. 12,14,15,16,17 It holds especial interest in connection with disease states that affect the excitability of spinal motoneurons. The present investigation deals with the H reflex in normal subjects and in patients with spasticity or rigidity. Material and Methods