The purpose of this study was to compare in amateur swimmers the critical swimming velocity (CV) with the swimming velocity corresponding to a blood lactate concentration of 4 mmol l−1 (V 4). Ten amateur swimmers volunteered for this study (six men, age 22.3 ± 2 years; four women, age 21.3 ± 1 years) and performed a 7 × 200-m swimming test (at 70%, 75%, 80%, 85%, 90%, 95% and 100% of their 200-m best time) with 5 min rest between each repetition. Blood lactate concentration was determined after each repetition. V 4 was determined from the speed-lactate curve. In order to calculate CV, the best front-crawl swimming results over 50, 100, 200 and 400 m were used. CV was expressed as the slope of the linear relationship between time and distance. Swimming velocities obtained with the two tests (CV 1.086 ± 0.151 m s−1; V 4 1.087 ± 0.128 m s−1) were positively and significantly correlated (r = 0.93, p < 0.05) and no significant differences were found. A Bland-Altman plot showed a good agreement between the two measurement methods. These results confirm that the CV seems to be a valid and noninvasive method for also determining training intensities and monitor endurance capacity in less-experienced athletes.