We investigated the effects of vitamin E supplementation on the time required to induce muscle fatigue in situ preparations of the sciatic nerve and gastrocnemius muscle of trained and sedentary rats. Four groups of animals were formed: sedentary non-supplemented (SWS), sedentary supplemented (SS), trained not supplemented (TWS) and trained supplemented (TS). The training was carried out with daily swimming sessions lasting 20 minutes for 4 weeks, with maximum load of 5% by weight and supplementation by intramuscular injection of 25 mg / kg on alternate days. Muscle fatigue was obtained by supramaximal tetanic nerve stimulation (50 Hz). For each muscle we evaluate the time necessary to reduce by 50% the maximal force (F50%) obtanined at the beginning of the tetanus. The F50% values were 33.33 ± 6,29 and 160,40 ± 44.34 sec for the group SWS and SS, respectively. The F50% values for the groups TWS and TS were respectively, 55.55 ± 16.33 and 142.22 ± 43.48 se. The differences between SWS and SS and TWS and TS were statistically significant. No significant differences were obtained between TS and SS and TWS and SWS. These data demonstrate that vitamin E increases the time required for the induction of muscle fatigue.