The H Reflex in Normal, Spastic, and Rigid Subjects

Abstract

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.^11,13Since 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. <h3>Material and Methods</h3>