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

TL;DR

This study found that the lactate-minimum approach does not reliably produce a stable lactate level during a 30-minute run in trained male middle-distance runners.

Contribution

The study introduces a new assessment of lactate stability using the minimum lactate steady state velocity in trained runners.

Findings

Blood lactate levels showed significant fluctuations during the 30-minute run at vMLaSS intensity.

Cardiopulmonary variables like V̇O₂ and V̇CO₂ remained stable during the trial.

Carbohydrate oxidation was the primary energy source, while fat oxidation was minimal.

Abstract

This study investigated the physiological behavior of the running velocity associated with the Minimum Lactate Steady State (vMLaSS), derived from a 6 × 800-m interval protocol, and examined whether this intensity produced stable metabolic and lactate responses during a 30-minute constant-load validation run in trained endurance runners.

Fifteen trained male middle- and long-distance runners completed a graded treadmill test to determine maximal oxygen uptake. Following a supramaximal sprint to induce hyperlactatemia, each athlete performed a 30-minute constant-load run at a velocity derived from the lactate-minimum approach. Following a supramaximal sprint to induce hyperlactatemia, each athlete performed a 30-minute constant-speed run at their individually determined MLaSS velocity. Blood lactate samples were collected at 10-minute intervals, and breath-by-breath cardiopulmonary variables were continuously recorded. Lactate kinetics were analyzed using a Friedman test with Wilcoxon signed-rank post-hoc comparisons (p < 0.05).

Blood lactate exhibited significant time-dependent fluctuations during the 30-minute trial (Friedman χ² (3) = 28.72, p < 0.001). Lactate increased sharply by minute 10, declined at minute 20, and rose again at minute 30, exceeding the classical MLSS criterion of ≤1 mmol·L ⁻ ¹ change during the final 20 minutes. In contrast, cardiopulmonary variables remained stable throughout V̇O₂ (3.43 ± 0.11 L·min ⁻ ¹; p = 0.86) and V̇CO₂ (3.21 ± 0.14 L·min ⁻ ¹; p = 0.91). Carbohydrate oxidation predominated (214.5 ± 19.3 g·h ⁻ ¹), whereas fat oxidation remained minimal (–0.9 ± 2.7 g·h ⁻ ¹).

Despite stable cardiorespiratory and substrate-utilization profiles, the significant variability in blood lactate concentration during the 30-minute constant-load run indicates that the running velocity derived from the lactate-minimum approach did not elicit a lactate steady state in this trained cohort. These findings suggest that physiological responses at the MLaSS-derived intensity may differ from classical steady-state expectations in highly trained endurance runners and highlight the need for direct MLSS verification in future studies.

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