The slow component of the [Formula: see text] response is associated with the increase in glycolytic contribution

After approximately 2 min of severe intensity exercise, there is a delayed increase in oxygen uptake (V̇O₂). It has been hypothesized that this slow component may be in response to an increase in glycolytic contribution, which causes a progressive recruitment of less-efficient Type II fibers. We examined whether the area under the curve of the V̇O₂ slow component (AUC_slow) is associated with glycolytic contribution during severe intensity constant-power cycling.

Seven women and 13 men completed three constant-power cycle tests terminated at 3, 6, or 9 min in randomized order. The kinetics of the V̇O₂ response was modelled using iterative regression, and AUC_slow was calculated. Glycolysis contribution was estimated from peak post-exercise blood lactate. Pearson correlations assessed associations at each duration.

AUC_slow was 2 ± 1 mL·kg⁻¹ in 0-3 min of exercise; there was an additional 8 ± 3 mL·kg⁻¹ in min 3-6 and an additional 4 ± 3 mL·kg⁻¹ in min 6-9. Glycolysis contribution was 18 ± 7 mL·kg⁻¹ in min 0-3, an additional 6 ± 2 mL·kg⁻¹ in min 3-6, and an additional 2 ± 1 mL·kg⁻¹ in min 6-9. Correlation values for AUC_slow and glycolytic contribution were strong (r = 0.69, p < 0.01 for 3-6 min; and r = 0.75, p < 0.01 for 6-9 min).

AUC_slow is related to glycolytic contribution after 3 min of severe intensity exercise. We speculate this is due to an increase in Type II fiber recruitment to compensate for fatiguing active fibers due to the accumulation of glycolytic metabolites.