AbstractIn order for the balance between lactic acid production and removal ratios to be maintained during long-distance races in performance swimming, endurance training sessions should be designed by taking due account of rest intervals. In this paper, we emphasize the importance of the aerobic metabolism in swimming races - swimming being based to a large extent on endurance. Moreover, our aim is to define some methodological aspects based on which we can build sets of exercises for developing endurance, by reconsidering rest breaks.