The purpose of this study was to understand the ventilatory and physiological responses immediately below and above the maximal lactate steady state velocity (MLSS) and to determine the relationship of oxygen uptake (V[Combining Dot Above]O2) kinetics parameters to performance, in swimmers. Competitive athletes (N = 12) completed in random order and different days a 400-m all-out test, an incremental step test comprising by 5 x 250 and 1 x 200-m stages and 30-min at constant swimming velocity at 87.5, 90 and 92.5% of maximal aerobic velocity (MAV) for MLSS velocity (MLSSv) determination. Two square wave transitions of 500-m, 2.5% above and below MLSSv were completed to determine V[Combining Dot Above]O2 on-kinetics. End-exercise V[Combining Dot Above]O2 at 97.5% and 102.5% of MLSSv represented, respectively, 81% and 97% of V[Combining Dot Above]O2max, the latter was not significantly different from maximal V[Combining Dot Above]O2 (V[Combining Dot Above]O2max). V[Combining Dot Above]O2 at MLSSv (49.3 +/- 9.2 ml.kg-1.min-1) was not significantly different from the second ventilatory threshold (VT2) (51.3 +/- 7.6 ml.kg-1.min-1). MLSSv seems to be accurately estimated by the swimming velocity at VT2 (vVT2) and vV[Combining Dot Above]O2max also seems to be estimated with accuracy from the central 300-m mean velocity of a 400-m trial, indicators that represent a helpful tool for coaches. 400-m swimming performance (T400) was correlated with the time constant of the primary phase V[Combining Dot Above]O2 kinetics ([tau]p) at 97.5% MLSSv and T800 was correlated with [tau]p in both 97.5% and 102.5% of MLSSv. The assessment of the V[Combining Dot Above]O2 kinetics in swimming can help coaches to build the training sets accordingly to the swimmer individual physiological response.
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