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Changes in Blood Lactate Concentration During a Step Incremental Test Do Not Predict Changes in Substrates Oxidation
José Antonio Benítez-Muñoz1, Pablo R Fleitas-Paniagua2,3, Juan M Murias4
1LFE Research Group, Department of Health and Human Performance, Faculty of Physical Activity and Sport Science (INEF), Universidad Politécnica de Madrid, Madrid, Spain.
Journal of Strength and Conditioning Research
|December 16, 2025
Summary
Changes in blood lactate concentration (La-) can indicate fat oxidation (FatOx) and carbohydrate oxidation (CHOx) if they remain stable. However, changes in La- do not predict changes in substrate oxidation as the training season progresses.
Area of Science:
- Exercise Physiology
- Sports Science
- Metabolic Research
Background:
- Blood lactate concentration (La-) is often used as an indirect marker for substrate oxidation during exercise.
- Understanding how substrate utilization changes throughout a training season is crucial for optimizing performance and training strategies.
Purpose of the Study:
- To investigate if changes in blood lactate concentration (La-) can predict changes in fat oxidation (FatOx) and carbohydrate oxidation (CHOx) over a training season.
- To assess the relationship between La-, FatOx, and CHOx in men and women at different points in a training period.
Main Methods:
- Fourteen men and 10 women underwent a step incremental exercise test on a cycle ergometer.
- Blood lactate concentration was measured at each stage and task failure.
- Fat oxidation (FatOx) and carbohydrate oxidation (CHOx) were estimated using indirect calorimetry during the last minute of each stage.
- Changes in La-, FatOx, and CHOx were calculated between two testing points (spring and fall).
Main Results:
- At each testing point, La- was strongly inversely associated with FatOx and strongly positively associated with CHOx.
- However, the changes in La- (Δ[La-]) showed a broad range of correlations with changes in FatOx (ΔFatOx) and CHOx (ΔCHOx) between the testing periods.
- These correlations were not significant, indicating a lack of predictive power for changes in substrate oxidation.
Conclusions:
- Blood lactate concentration (La-) can serve as an indirect measure of substrate oxidation if La-, FatOx, and CHOx remain stable throughout the training season.
- Crucially, changes in blood lactate concentration do not predict alterations in fat and carbohydrate oxidation as the training season progresses.
- This highlights the limitation of using lactate alone to monitor training-induced adaptations in substrate metabolism over time.
