Maximal glycolytic flux modulates metabolic thresholds independent of maximal oxygen uptake

This study examined how maximal glycolytic flux, indexed by the peak lactate accumulation rate (vLa_peak) from a 15-s sprint, relates to lactate- and gas-exchange derived endurance thresholds at a given V̇O₂max in trained cyclists.

Fifty cyclists (30 men, 20 women) completed two laboratory visits: a ramp test with verification to determine V̇O₂max, and on a separate day, a 15-s all-out sprint with repeated post-exercise capillary blood sampling to determine peak lactate accumulation (ΔLa) and derived vLa_peak, followed by a 3-min step-increment test with lactate and gas-exchange measurements.

Partial correlations controlling for V̇O₂max revealed moderate-to-strong negative associations between vLa_peak and selected lactate- and gas-exchange-derived thresholds (r = - 0.37 to - 0.59, p < 0.01), whereas absolute and relative 15-s work showed consistently weaker or no relationships (r = 0.06 to - 0.48). No association was observed between vLa_peak and peak fat oxidation. In general linear models, adding vLa_peak to models with V̇O₂max and sex as predictors significantly increased the explained variance in threshold power (ΔR² ≈ 0.06 to 0.20). Sex contributed additional but consistently smaller effects.

These findings indicate that the power output at several metabolic thresholds originates from the interaction of maximal oxidative and glycolytic flux. As such, vLa_peak seems to be a promising parameter that complements traditional measures like V̇O₂max and helps to improve metabolic profiling and exercise prescription. However, longitudinal studies are needed to verify these findings.