Maximal glycolytic flux modulates metabolic thresholds independent of maximal oxygen uptake

Abstract Purpose This study examined how maximal glycolytic flux, indexed by the peak lactate accumulation rate ( v La peak ) from a 15-s sprint, relates to lactate- and gas-exchange derived endurance thresholds at a given V̇O 2 max in trained cyclists. Methods Fifty cyclists (30 men, 20 women) completed two laboratory visits: a ramp test with verification to determine V̇O 2 max, 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 v La peak , followed by a 3-min step-increment test with lactate and gas-exchange measurements. Results Partial correlations controlling for V̇O 2 max revealed moderate-to-strong negative associations between v La 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 v La peak and peak fat oxidation. In general linear models, adding v La peak to models with V̇O 2 max and sex as predictors significantly increased the explained variance in threshold power (ΔR 2 ≈ 0.06 to 0.20). Sex contributed additional but consistently smaller effects. Conclusion These findings indicate that the power output at several metabolic thresholds originates from the interaction of maximal oxidative and glycolytic flux. As such, v La peak seems to be a promising parameter that complements traditional measures like V̇O 2 max and helps to improve metabolic profiling and exercise prescription. However, longitudinal studies are needed to verify these findings.