The relationship between critical velocity, maximal lactate steady-state velocity and lactate turnpoint velocity in runners

In cycle exercise, it has been suggested that critical power, maximal lacta te steady state, and lactate turnpoint all demarcate the transition between the heavy exercise domain (in which blood lactate is elevated above restin g values but remains stable over time) and the very heavy exercise domain ( in which blood lactate increases continuously throughout constant-intensity exercise). The purpose of the present study was to assess the level of agr eement between critical velocity (CV), maximal lactate steady-state velocit y (MLSSV), and lactate turnpoint velocity (LTPV) during treadmill running. Eight male subjects [mean (SD) age 28 (5) years, body mass 71.2 (8.0) kg, m aximum oxygen uptake 54.9 (3.2) ml.kg(-1).min(-1)) performed an incremental treadmill test for the determination of LTPV (defined as a sudden and sust ained increase in blood lactate concentration ([La]) at congruent to2.0-5.0 mM). The subjects returned to the laboratory on eight or nine occasions fo r the determination of CV and MLSSV. The CV was determined from four treadm ill runs at velocities that were chosen to result in exhaustion within 2-12 min. The MLSSV was determined from four or five treadmill runs of up to 30 min duration and defined as the highest velocity at which blood [La] incre ased by no more than 1.0 mM after between 10 and 30 min of exercise. Analys is of variance revealed no significant differences between [mean (SD)] CV [ 14.4 (1.1) km.h(-1)], MLSSV [13.8 (1.1) km.h(-1)] and LTPV [13.7 (0.6) km.h (-1)]. However, the bias +/- 95% limits of agreement for comparisons betwee n CV and MLSSV [0.6 (2.2) km.h(-1)], CV and LTPV [0.7 (2.7) km.h(-1)], and MLSSV and LTPV [0.1 (1.8) km.h(-1)] suggest that the extent of disagreement is too great to allow one variable to be estimated accurately from another in individual subjects. Direct determination of MLSSV is necessary if prec ision is required in experimental studies.