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The relationship between excess CO2 and blood lactate in elite cyclists Anderson, Gregory Steven


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 <0.001) stress the individual nature of this relationship. Expired EXCO₂ volume appeared to track blood lactate levels over this 11 minute period when the significant threshold difference (1.35 min.) was taken into consideration. These results indicate a strong relationship between the three threshold values, although changes and expired EXCO₂ precede changes in blood lactate concentration and the ventilatory equivelant (VE/VO₂). Although changes in expired EXCO₂ volume appear to track changes in blood lactate concentration, blood lactate concentration can not be accurately predicted from expired EXCO₂ volume as the nature of this relationship varies between individuals and. appears to be influenced by gender.

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