Maximal lactate steady state, respiratory compensation threshold and critical power

Critical power (CP) and the second ventilatory threshold (VT2) are presumed to indicate the power corresponding to maximal lactate steady state (MLSS). The aim of this study was to investigate the use of CP and VT2 as indicators of MLSS. Eleven male trained subjects [mean (SD) age 23 (2.9) years] performed an incremental test (25 W·minm1) to determine maximal oxygen uptake (V£O2max), maximal aerobic power (MAP) and the first and second ventilatory thresholds (VT1 and VT2) associated with break points in minute ventilation (V£E), carbon dioxide production (V£CO2), V£E/V£CO2 and V£E/V£O2 relationships. Exhaustion tests at 90%, 95%, 100% and 110% of V£O2max and several 30-min constant work rates were performed in order to determine CP and MLSS, respectively. MAP and V£O2max values were 344 (29) W and 53.4 (3.7) ml·minm1·kgm1, respectively. CP [278 (22) W; 85.4 (4.8)% V£O2max] and VT2 power output [286 (28) W; 85.3 (5.6)% V£O2max] were not significantly different (p=0.96) but were higher (p<0.05) than the MLSS work rate [239 (21) W; 74.3 (4.0)% V£O2max] and VT1 power output [159 (23) W; 52.9 (6.9)% V£O2max]. MLSS work rate was significantly correlated (p<0.05) with those noted at VT1 and VT2 (r=0.74 and r=0.93, respectively). VT2 overestimated MLSS by 10.9 (6.3)% V£O2max which was significantly higher than VT1 [+21.4 (5.6)% V£O2max; p<0.01]. CP calculated from a given range of exhaustion times does not correspond to MLSS.