Comparison of NIRS exercise intensity thresholds with maximal lactate steady state, critical power and rowing...

This study aimed to compare the intensity of deoxygenated haemoglobin concentration ([HHb]) and tissue saturation index (TSI) breakpoints ([HHb]-BP and TSI-BP) with maximal lactate steady state (MLSS) and critical power (CP), and to describe their association with 2000-m rowing ergometer performance. Fourteen male rowers performed on a rowing ergometer: I) a discontinuous incremental test with 3-min stages (INC₃); II) a continuous incremental test with 1-min stages (INC₁); III) constant workload tests to determine MLSS; and IV) performance tests of 500 m, 1000 m, 2000 m and 6000 m to determine CP.CP (257 ± 39 W; 3.79 ± 4.1 L · min^-1) was higher than [HHb]-BP₃ (205 ± 26 W; 3.48 ± 2.9 L · min^-1), [HHb]-BP₁ (207 ± 27 W; 3.27 ± 3.2 L · min^-1), and TSI-BP₃ (218 ± 31 W; 3.51 ± 3.0 L · min^-1), but not higher than TSI-BP₁ (222 ± 34 W; 3.43 ± 3.2 L · min^-1). MLSS (187 ± 26 W; 3.33 ± 3.2 L · min^-1) was lower than TSI-BP₃ and TSI-BP₁ for power output, but not different in any comparison for ⩒O₂. The limits of agreement for power output and ⩒O₂ suggest poor agreement among these thresholds. The low level of agreement compromises the use of [HHb]-BP and TSI-BP for estimating MLSS and CP; therefore, these thresholds should not be considered interchangeable.