Relationship between blood lactate and excess CO₂ in elite cyclists

Abstract

This study examined the relationship between expired non‐metabolic CO₂ (exCO₂) and the accumulation of blood lactate. Particular emphasis was placed on the ventilatory (exCO₂ and VE/VO₂) and lactate threshold relationship. A total of 21 elite cyclists (15 males, 6 females) performed a progressive intensity bicycle ergometer test during which ventilatory parameters were monitored online at 15‐s intervals, and blood lactate sampling occurred at each minute. Transition threshold values were determined for each of the three indices: excess CO₂ (T_{exCO 2} ), VE/VO₂ (r_vent) and blood lactate (T _lac). The three threshold values (T_{exCO 2} , T _vent, T _lac) all correlated significantly (P <0.001) when each was expressed as an absolute VO ₂ (1 min^‐1). A significant ANOVA (F = 8.41, P <0.001) and post‐hoc correlated (‐tests demonstrated significant differences between the T _exCO2 and T _lac (P <0.001) and the T _exCO2 and T _vent values (P <0.025).

The T _lac occurred at an average blood lactate concentration of 3.35 mni, while the mean expired excess CO₂ volume at the T _exCO2 was 14.04 ml kg^‐1 min^‐1.Overan 11‐min range across the threshold values (T_exCO2 and T _lac), which were used as relative points of reference, the expired excess CO₂ volume (ml kg^‐1 min^‐1) and blood lactate concentration (mm) correlated significantly (r = 0.69, P <0.001). Higher individual correlations over the same period of time (r = 0.82–0.96, P <0.001) stress the individual nature of this relationship. These results indicate a strong relationship between the three threshold values. Changes in expired excess CO₂ precede changes in blood lactate concentration and the ventilatory equivalent (VE/VO₂). Although changes in expired excess CO₂ volume appear to track changes in blood lactate concentration, blood lactate concentration cannot be accurately predicted from expired excess CO₂ volume as the nature of this relationship varies between individuals and appears to be influenced by gender.

Keywords:

• Blood lactate
• excess CO₂
• elite cyclists
• ventilatory thresholds