Maximal lactate steady state, respiratory compensation threshold and critical power

Critical power (CP) and the second ventilatory threshold (VT(2)) 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 VT(2) as indicators of MLSS. Eleven male trained subjects [mean (SD) age 23 (2.9) years] performed an incremental test (25 W.min(-1)) to determine maximal oxygen uptake (.VO(2max)), maximal aerobic power (MAP) and the first and second ventilatory thresholds (VT(1) and VT(2)) associated with break points in minute ventilation (.V(E)), carbon dioxide production (.VCO(2)), .V(E)/.VCO(2) and .V(E)/.VO(2) relationships. Exhaustion tests at 90%, 95%, 100% and 110% of .VO(2max), and several 30-min constant work rates were performed in order to determine CP and MLSS, respectively. MAP and .VO(2max) values were 344 (29) W and 53.4 (3.7) ml.min(-1).kg(-1), respectively. CP [278 (22) W; 85.4 (4.8)% .VO(2max)] and VT(2) power output [286 (28) W; 85.3 (5.6)% .VO(2max)] 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)% .VO(2max)] and VT(1) power output [159 (23) W; 52.9 (6.9)% .VO(2max)]. MLSS work rate was significantly correlated (p<0.05) with those noted at VT(1) and VT(2) (r=0.74 and r=0.93, respectively). VT(2) overestimated MLSS by 10.9 (6.3)% .VO(2max), which was significantly higher than VT(1) [+21.4 (5.6)% .VO(2max); p<0.01]. CP calculated from a given range of exhaustion times does not correspond to MLSS.