Failure to obtain a unique threshold on the blood lactate concentration curve during exercise

The purpose of this study was to compare various methods and criteria used to identify the anaerobic threshold (AT), and to correlate the AT obtained with each other and with running performance. Furthermore, a number of additional points throughout the entire range of lactate concentrations [La-] were obtained and correlated with performance. A group of 19 runners [mean age 33.7 (SD 9.6) years, height 173 (SD 6.3) cm, body mass 68.3 (SD 5.4) kg, maximal O2 Uptake (VO2max) 55.2 (SD 5.9) ml x kg(-1) x min(-1)] performed a maximal multistage treadmill test (1 km x h[-1] every 3.5 min) with blood sampling at the end of each stage while running. All AT points selected (visual [La-], 4 mmol x l(-1) [La-], 1 mmol x l(-1) above baseline, log-log breakpoint, and 45 degrees tangent to the exponential regression) were highly correlated one with another and with performance (r > 0.90) even when there were many differences among the AT (P < 0.05). The additional points (ranging from 3 to 8 mmol x l(-1) [La-], 1 to 6 mmol x l(-1) [La-] above the baseline, and 30 to 70 degrees tangent to the exponential curve of [La-]) were also highly correlated with performance (r > 0.90). These results failed to demonstrate a distinct AT because many points of the curve provided similar information. Intercorrelations and correlations between AT and performance were, however, reduced when AT were expressed as the percentage of maximal treadmill speed obtained at AT or percentage of VO2max. This would indicate that different attributes of aerobic performance (i.e. maximal aerobic power, running economy and endurance) are measured when manipulating units. Thus, coaches should be aware of these results when they prescribe an intensity for training and concentrate more on the physiological consequences of a chosen [La-] rather than on a "threshold".