The relationship between excess CO2 and blood lactate in elite cyclists

This study examined the relationship between expired non-metabolic CO₂ (EX CO₂) and the accumulation of blood lactate, while emphasis was placed on the ventilatory (EX CO₂ and VE/VO₂) and lactate threshold relationship. Twenty-one elite cyclists (15 males, 6 females) performed a progressive intensity bicycle ergometer test (PIT) during which ventilatory parameters were monitored on-line at 15 second intervals, and blood lactate sampling occured on each minute. Threshold values were determined for each of the three indices; excess CO₂ (EXTT), VE/V0₂ (VVTT), and blood lactate (LATT). The three threshold values (EXTT, VVTT, LATT) all correlated significantly (P<0.001) when each was expressed as an absolute VO₂ (1/min). A significant RM ANOVA (F=8.41, P<0. 001) and post hoc correlated t-tests demonstrated significant differences between the EIXTT and LATT (P<0.001) and the EXTT and VVTT values (P<0.025). The LATT occured at an average blood lactate concentration of 3.35 mmol/1, while the mean expired excess CO₂ volume at the EXTT was 14.04 ml/kg/min. Over an 11 minute range across the threshold values (EXTT and LATT), which were used as relative points of reference, the expired EXC02 volume (ml/kg/min) and blood lactate concentration (mmol/1) correlated significantly (r=0. 69, P<0. 001). Higher individual correlations over the same period of time <r=0.82 - 0.96, P