Relationship between blood lactate and excess CO2 in elite cyclists

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 (TexCO2), VE/VO2 (rvent) and blood lactate (Tlac). The three threshold values (TexCO2, Tvent, Tlac) all correlated significantly (P 0.001) when each was expressed as an absolute VO2 (1 min-1). A significant ANOVA (F = 8.41, P 0.001) and post-hoc correlated (-tests demonstrated significant differences between the TexCO2 and Tlac (P 0.001) and the TexCO2 and Tvent values (P 0.025). The Tlac occurred at an average blood lactate concentration of 3.35 mni, while the mean expired excess CO2 volume at the TexCO2 was 14.04 ml kg-1 min-1.Overan 11-min range across the threshold values (TexCO2 and Tlac), 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.