Do 5% changes around maximal lactate steady state lead to swimming biophysical modifications?

•V̇O2, Ė and C remain constant as a function of time at intensities up to MLSS.•V̇O2, Ė and C still remain constant as a function of time at 102.5%MLSS.•Hyperventilation and decreased OUE are observed as a function of time at 102.5%MLSS.•Biomechanics factors are compromised as a function of time at 102.5%MLSS.•Bioenergetical and biomechanics changes at 102.5%MLSS reduce swim ability. Our purpose was to examine the swimming biophysical responses at velocities (v) of 97.5, 100 and 102.5% of the maximal lactate steady state (MLSS). Ten elite female swimmers performed three-to-five 30-min constant tests at imposed paces to determine 97.5, 100 and 102.5%MLSS v. Gas exchange, blood lactate concentration ([La-]), stroke rate (SR) and v were determined during each test. The v values at 97.5, 100 and 102.5%MLSS were 1.21±0.07, 1.24±0.07 and 1.27±0.07m.s−1, respectively. Oxygen uptake (V̇O2) and Pulmonary ventilation (V̇E) increased as function of v. SR and stroke length (v/SR=SL) increased as a function of v. All measured variables were constant as a function of time at 97.5%MLSS and 100%MLSS. At 102.5%MLSS SR increased (3.5%) and stroke length (SL) decreased (3.5%) as a function of time. While V̇O2 was constant at 102.5%MLSS, [La-] and V̇E increased as a function of time, suggesting hyperventilation, at v’s of 97.5%MLSS and 100%MLSS swimmers completed the 30min swim in spite of decreased SL and increased SR. However, the decrease in SL and increased SF were accompanied by increased [La-] and V̇E and resulted in the inability of most swimmers to complete the 30min swim presumably due to fatigue at 102.5%MLSS.