Introduction: The maximum lactate steady state (MLSS) represents the highest intensity of exercise at which a balance exists between the rate of lactate production and the rate of lactate clearance. The MLSS is an important determinant of endurance exercise performance but its determination, which involves 4-5 laboratory visits, is labor-intensive and time consuming.
Purpose: To compare the MLSS estimated from a single-visit protocol (MLSSsingle) with the traditional, directly measured MLSS (MLSStrad).
Methods: Following an incremental treadmill test for the determination of VO2peak, eight endurance-trained runners completed: 1) a series of 4-5 constant-speed treadmill runs of up to 30-min duration, on separate days, for determination of the MLSStrad; and 2) a single-visit protocol consisting of two constant-speed treadmill runs of 20-min duration at approximately 65 and 90% VO2peak separated by 40 min of rest, for determination of MLSSsingle. Blood lactate concentration ([La]), oxygen uptake (VO2), and heart rate (HR) were measured every 5 min in all treadmill runs. Comparisons between values were made using paired t-tests.
Results: The MLSSsingle significantly underestimated the MLSStrad with respect to speed (13.4 +/- 1.2 vs 16.4 +/- 1.6 km x h(-1), P = 0.002), HR (148 +/- 8 vs 170 +/- 10 b x min(-1), P < 0.001), blood [La] (2.3 +/- 1.5 vs 3.9 +/- 1.0 mmol x L(-1); P = 0.01), and % VO2peak utilized (75 +/- 8 vs 90 +/- 2%, P = 0.002). The MLSStrad speed and MLSSsingle speed were poorly correlated (r = 0.29, P = 0.49).
Conclusion: The single-visit method of determining the MLSS substantially underestimates the actual MLSS.