Purpose The aim of this study was to analyze the acute responses of oxygen uptake and its kinetics, blood lactate concentration, total metabolic energy and energetic contributions to swimming tests performed at 90%, 92.5% and 95% of the 400m front crawl test mean speed. Methods Fourteen male swimmers (26.7 ± 5.4 years) performed a 400m front crawl test and three swimming sets at 90%, 90.5%, and 95% of the mean 400m test swimming speed. Oxygen uptake, blood lactate concentration, oxygen uptake kinetics (amplitude, time in seconds of the fast phase, time delay and constant time adjustment in the fast phase), total metabolic energy and energetic contributions were obtained. Descriptive and inferential statistics were applied. Results Among the results, the oxygen uptake and time in the 400m test were: 55.0 ± 5.8ml.kg-1.min-1 and 324.2 ± 20.0s. At 90, 92.5 and 95% sets, the oxygen uptake was, respectively, 45.6 ± 4.4, 49.0 ± 6.0, and 52.4 ± 5.8ml.kg-1.min-1. For 90%, 90.5%, and 95%, total time to exhaustion was, respectively: 1466.1 ± 730.9; 888.71 ± 324.0 and 562.7 ± 166.6s. The amplitude of the kinetics was higher at 95% set. The slow component of the VO2 kinetics on the 90%, 92.5% and 95% sets were, respectively: 120.7 ± 82.9ml.min-1, 171.8 ± 140.6ml.min-1, and 182.6 ± 120.2ml.min-1. No differences were identified among the slow component`s values. Aerobic contribution was predominant and has decreased as the intensity increased. Conclusion The results suggest that, as there was an increase in intensity (90%, 92.5%, and 95%): (i) increase in oxygen uptake, in blood lactate concentration, in the amplitude of oxygen uptake kinetic; and (ii) decrease in total metabolic energy. Regarding the aerobic and anaerobic percentage contribution, as expected, as the intensity of the exercise increased, the aerobic percentage decreased, in turn, the anaerobic component increased.
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