INTRODUCTION: The number of studies directly determining velocity at the maximal lactate steady state (MLSSv) in swimming is quite limited and its correspondence to critical velocity (CV), implied by well accepted physiological models, has not been proven, contrarily to what has been found for other types of human locomotion. The purpose of this study was to compare CV to the MLSSv in swimming. METHODS: Eighteen male national and international level competitive swimmers performed a maximal 400 m front crawl in order to estimate maximal aerobic velocity (V400). CV was calculated from the slope of the regression analysis between the averaged velocity of the 400 m trial and a 200 m front crawl maximal trial performed for this purpose. All swimmers completed, in random order and in different days, 30-min swims at constant intensity (85, 90 and 85% of V400) for the determination of MLSSv and also of stroke parameters and rate of perceived exertion at MLSS. RESULTS: MLSSv corresponded to 89.7±1.2% and CV to 94.0±1.5% of V400. Only one swimmer achieved MLSS at 85% of V400. Extreme values of 2.6 and 7.8 mmol.L-1 were found associated to MLSSv. CV was significantly faster than MLSSv (p<0.01) and both expressed velocities significantly different from V400 (p<0.01). MLSSv and CV were highly correlated (r=0.94; p<0.01). Both were associated with V400 (r=0.97, p<0.01 and r=0.95, p<0.01, respectively). Linear regression of MLSSv on CV (MLSSv=0.78 CV + 0.25; SSE=0.02 m.s-1) revealed that the latter can be predicted with reasonable accuracy from the 200 m / 400 m swim trials CV. Stroke cycle parameters were unrelated to performance, MLSSv or CV. DISCUSSION: MLSS can be achieved using two to three 30- min constant velocity swims. Our results confirm the finding of previous studies that CV overestimates MLSSv in swimmers showing that this parameter does not represent a steady metabolic rate in long distance swimming. Therefore, it appears that CV in swimmers does not demarcate the transition from heavy to severe exercise and may not provide a direct noninvasive measure of MLSSv. However, our data also indicates that MLSSv could be estimated from CV with enough accuracy to be used in training exercises prescription. This has important practical implications, since CV still seems to be a useful tool for aerobic conditioning evaluation, due to the simplicity of its determination.
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