The mammalian nervous system processes complex information to control complex behaviors. Since the speed of transport of information can be a life-saving phenomenon, it is extremely important to stabilize the rate of these processes. This study aims to investigate the protective effects of melatonin supplementation on acute heavy exercise-induced changes in the nerve conduction velocity distributions (CVD). Remodeling of the sciatic nerve due to heavy exercise demonstrates not only an increase in some parameters (rheobase and chronaxie), but also decreases in maximum depolarization, total area under the compound action potential (CAP), fall-down phase of CAP kinetics and speed of the intermediately conducting group. Acute heavy exercise-induced decreases in the contribution of nerve fibers were mainly found between 1.0 and 1.7 interstimulus interval (ISI) values (46-52 m/s). Presupplementation with melatonin, a powerful antioxidant for nervous tissues, protects the sciatic nerve against all of the aforementioned changes. Presupplementation not only protects the nerve cells from exercise-induced damage, but also increases the contribution of nerve fibers with conduction velocities of 46-52 m/s. Copyright © 2009 Prous Science, S.A.U. or its licensors. All rights reserved.