Resolving Differences between MLSS and CP by Considering Rates of Change of Blood Lactate during Endurance Exercise.

Abstract

Purpose: This study aimed to develop a new method that more closely represents the heavy to severe exercise domain boundary by evaluating the rates of blood lactate accumulation during the constant power output exercise bouts that are used in the assessment of the maximal lactate steady state (MLSS).

Methods: Eight well-trained male cyclists completed five exercise tests of up to 30 min for the determination of the traditional MLSS (MLSS TRAD ) and a further four maximal tests for the determination of critical power (CP). The rates of change of blood [lactate] between 10 min and the end of exercise in the MLSS tests were plotted against the corresponding power outputs, and a two-segment linear regression model was used to identify individualized break points in lactate accumulation versus power output (modified MLSS [MLSS MOD ]).

Results: MLSS MOD was significantly higher than MLSS TRAD (297 ± 41 vs 278 ± 41 W, P < 0.001) but was not significantly different from CP (297 ± 41 W, P > 0.05); MLSS MOD and CP were closely aligned ( r = 0.97, bias = -0.52 W, SEE = 10 W, limits of agreement = -20 to 19 W). The rates of change of both blood [lactate] and V̇O 2 were significantly greater, and exercise intolerance occurred before 30 min, at a power output slightly above MLSS MOD .

Conclusions: A novel method for evaluating blood lactate kinetics during MLSS TRAD protocol produces MLSS MOD that is not different from CP and better represents the heavy to severe exercise domain boundary.