Identification of Lactate Threshold
The identification of lactate threshold can be of significant value in both applied and research settings. Both practitioners and researchers commonly refer to the lactate threshold. Coaches and endurance athletes wanting to use physiological principles in their training programs and researchers desiring a sensitive marker of endurance capacity both use the lactate threshold as a point of reference for exercise intensity. Literature involving the lactate threshold has been controversial and often times confusing due to the various methods used to identify the specific point of lactate threshold. The following is an overview of several methods used to identify lactate threshold that are commonly seen throughout the applicable literature.
Visual inspection:
Use of the visual method involves determining the specific level of exercise intensity at the point where a visibly noticeable rise in blood lactate concentration occurs. A number of authors use “visual inspection” of the changes in blood lactate concentration plotted in relation to exercise intensity (Carter, Jones, & Doust, 2000; Farrell et al., 1979; Pierce, Weltman, Seip, & Snead, 1990; Roecker et al., 1998; Vachon, Bassett, & Clarke, 1999; Wiswell et al., 2000). The reliability and validity of this method may be questionable due to the subjective nature of this method. However, it is an accepted and commonly used method.
Specific elevations in blood lactate above resting level:
Several researchers have used pre-selected specific elevations in blood lactate concentration as a method of determining lactate threshold. Yoshida, Chida, Ichioka and Suda (1987) used 1 mmol·L-1 above the resting level while Coyle et al. (1983) used 1 mmol·L-1 above the exercise baseline as their determinate of lactate threshold. In practice, both of these methods should give the same point since resting and mild intensity blood lactate levels are consistently similar. These methods are often referred to as “delta 1” methods.
Specific increases in blood lactate between workloads:
Thoden suggests identifying lactate threshold as the first occurrence of consecutive increases in blood lactate 1 mmol·L-1 (Thoden, 1991). Similar or larger increases in lactate values must occur during the next increment of work. When using this method the work increment that immediately precedes the initial rise of blood lactate greater than or equal to 1 mmol·L-1, is chosen as the lactate threshold. This has also been termed a “delta 1” method.
D-max Method:
Cheng et al. (1992) developed a method for the determination of a threshold point. This method involves computing the point on a regression curve “that yields the maximum distance to the line formed by the two end points of the curve”. The point associated with the maximum perpendicular distance between the lactate curve and this straight line formed by the two ends of that curve is identified as the point of threshold. The objectivity of this method has a strong appeal to researchers.
Log-log transformation:
This method is a mathematical model, which offers more objectivity and has become widely accepted. Beaver, Wasserman and Whipp (1985) determined that the generation of linear regressions plotting the blood lactate concentration relationship against exercise intensity was a valid method of determining lactate threshold. The use of this method involves plotting lactate concentration against O2 at each workload. Two distinct phases of lactate concentration as a function of workload are observed with this method. The intersection of the lines of best fit for these two phases is determined to be the lactate threshold. Beaver et al. found these phases to be linear on the log-log plot, determining that linear regression analysis may therefore be used to locate the transition between them.
Fixed blood lactate concentrations:
Concentration levels of 2.0, 2.5, 3.0 and 4.0 mmol·L-1 are all values at which the “lactate threshold” term has been used. The 4.0 level of blood lactate concentration is the most often referenced “lactate threshold” and is often referred to as the Onset of Blood Lactate Accumulation or OBLA. Potential confounders may exist using fixed blood lactate concentrations.
METHODS OF IDENTIFYING LACTATE THRESHOLD