Assessing lactate stability at the minimum lactate steady state velocity in male trained middle-distance runners.

Blood lactate exhibited significant time-dependent fluctuations during the 30-minute constant-load run at the MLaSS-derived velocity.

• Friedman χ² (3) = 28.72, p < 0.001
• Lactate increased sharply by minute 10, declined at minute 20, and rose again at minute 30
• The lactate change exceeded the classical MLSS criterion of ≤1 mmol·L⁻¹ during the final 20 minutes
• 15 trained male middle- and long-distance runners participated
• Blood lactate samples were collected at 10-minute intervals (0, 10, 20, and 30 minutes)

Cardiopulmonary variables remained stable throughout the 30-minute constant-load run at the MLaSS-derived velocity.

• VO₂ was 3.43 ± 0.11 L·min⁻¹ with p = 0.86
• VCO₂ was 3.21 ± 0.14 L·min⁻¹ with p = 0.91
• Breath-by-breath cardiopulmonary variables were continuously recorded throughout the trial
• Cardiorespiratory stability contrasted with the significant lactate variability observed over the same period

Carbohydrate oxidation predominated during the constant-load run at MLaSS-derived velocity, while fat oxidation remained minimal.

• Carbohydrate oxidation was 214.5 ± 19.3 g·h⁻¹
• Fat oxidation was -0.9 ± 2.7 g·h⁻¹
• Substrate utilization profiles were stable throughout the 30-minute trial
• The predominance of carbohydrate oxidation is consistent with the high-intensity nature of the MLaSS-derived velocity

The study protocol used a 6 × 800-m interval protocol to derive the MLaSS velocity, preceded by a supramaximal sprint to induce hyperlactatemia.

• A graded treadmill test was completed to determine maximal oxygen uptake prior to the lactate-minimum protocol
• The supramaximal sprint was used to induce hyperlactatemia as part of the lactate-minimum approach
• The 30-minute constant-load validation run was performed at the individually determined MLaSS velocity
• Lactate kinetics were analyzed using a Friedman test with Wilcoxon signed-rank post-hoc comparisons (p < 0.05)

The running velocity derived from the lactate-minimum approach did not elicit a lactate steady state in this trained cohort, suggesting its physiological responses differ from classical steady-state expectations in highly trained endurance runners.

• Despite stable cardiorespiratory and substrate-utilization profiles, blood lactate concentration showed significant variability
• The lactate fluctuation pattern (rise at 10 min, decline at 20 min, rise again at 30 min) is inconsistent with classical MLSS behavior
• The authors highlight the need for direct MLSS verification in future studies
• Findings suggest the lactate-minimum approach may not be a valid surrogate for MLSS determination in highly trained runners