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

Area of Science:

• Exercise Physiology
• Sports Science
• Biochemistry

Background:

• The maximal lactate steady state (MLSS) is crucial for defining exercise intensity domains.
• Traditional MLSS (MLSS TRAD) assessment may not precisely delineate the boundary between heavy and severe exercise.
• Critical power (CP) is another key physiological threshold indicating the transition to severe exercise.

Purpose of the Study:

• To develop a novel method for determining MLSS that better represents the heavy to severe exercise domain boundary.
• To evaluate blood lactate accumulation rates during constant power output exercise to refine MLSS assessment.
• To compare the newly developed MLSS method with traditional MLSS and critical power.

Main Methods:

• Eight well-trained male cyclists performed exercise tests to determine MLSS TRAD and CP.
• A modified MLSS (MLSS MOD) was calculated by plotting blood lactate accumulation rates against power output using a two-segment linear regression model.
• Individualized break points in lactate accumulation versus power output were identified.

Main Results:

• MLSS MOD (297 ± 41 W) was significantly higher than MLSS TRAD (278 ± 41 W).
• MLSS MOD was not significantly different from CP (297 ± 41 W) and showed high correlation (r = 0.97).
• Rates of blood lactate and V̇O2 change were greater above MLSS MOD, with exercise intolerance occurring near this threshold.

Conclusions:

• The novel method (MLSS MOD) accurately reflects the heavy to severe exercise domain boundary.
• MLSS MOD is physiologically equivalent to CP, providing a more precise measure than MLSS TRAD.
• This approach enhances the understanding of exercise intensity domains and performance limitations.