Abstract: Espada, MC, Reis, JF, Almeida, TF, Bruno, PM, Vleck, VE, and Alves, FB. Ventilatory and physiological responses in swimmers below and above their maximal lactate steady state. J Strength Cond Res 29(10): 2836–2843, 2015—The purpose of this study was to understand the ventilatory and physiological responses immediately below and above the maximal lactate steady-state (MLSS) velocity and to determine the relationship of oxygen uptake (V[Combining Dot Above]O2) kinetics parameters with performance, in swimmers. Competitive athletes (N = 12) completed in random order and on different days a 400-m all-out test, an incremental step test comprising 5 × 250- and 1 × 200-m stages and 30 minutes at a constant swimming velocity (SV) at 87.5, 90, and 92.5% of the maximal aerobic velocity for MLSS velocity (MLSSv) determination. Two square-wave transitions of 500 m, 2.5% above and below the 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). The 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). The velocity associated with MLSS seems to be accurately estimated by the SV 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. The 400-m swimming performance (T400) was correlated with the time constant of the primary phase V[Combining Dot Above]O2 kinetics (τp) at 97.5% MLSSv, and T800 was correlated with τp 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 training sets according to a swimmer’s individual physiological response.