Taking into account that alcohol users represent a good portion of the human population, that the prolonged use of alcohol in excess causes multiplicity of both biochemical and morphological abnormalities, a study has been carried out on the effect of this drug in a mixture where alcohol represents more than 50% of the daily calories used by the rat, which presents a selective atrophy of Type II-fibers, similar to that in humans. Thus, a sample was collected from the rectus abdominalis muscle in five animals of each group: Control (C), Alcoholized (A) and Isocaloric (I). The samples were submitted to m-ATPase reactions (with acid and alkaline pre-incubations) and NADH-TR to classify the fibers according to the results obtained in these reactions. The results showed a significant difference in the frequency of Type-FG fibers, as well as in that of the type FOG, among the groups studied. As for the area, the results pointed to a significant difference just for the FG-type fibers, being smaller in the animals of group A and larger in those of group C. Based on this data, one may conclude that the alcoholization altered the size of Type-FG fibers and the frequency of fibers FG and FOG.

KEY WORDS: alcoholism; types of muscular fibers; rats – Rattus norvegicus; rectus abdominalis