Respiratory gas exchange indices used to detect the blood lactate accumulation threshold during an incremental exercise test in young athletes

Summary

The time course of changes in blood lactate concentration and ventilatory gas exchange was studied during an incremental exercise test on a cycle ergometer to determine if the lactate accumulation threshold (LT₂) could be accurately estimated by the use of respiratory indices (VT₂) in young athletes. LT₂ was defined as the starting point of accelerated lactate accumulation. VT₂ was identified by the second exponential increase in$\dot V$ _E and the ventilatory equivalent for O₂ uptake with a concomitant nonlinear increase in the ventilatory equivalent for CO₂ output. Twelve trained subjects, aged 18–22 years, participated in this study. The initial power setting was 30 W for 3 min with successive increases of 30 W every minute except at the end of the test when the increase was reduced. Ventilatory flow ($\dot V$ _E), oxygen uptake ($\dot V$O₂), carbon dioxide output ($\dot V$CO₂), and ventilatory equivalents of O₂ and CO₂ were determined during the last 30 s of every minute. Venous blood samples were drawn at the end of each stage of effort and analysed enzymatically for lactate concentration. After each test, LT₂ and VT₂ were determined visually by two investigators from the graphic results using a double-blind procedure. The results [mean (SEM)] indicate no significant difference between LT₂ and VT₂ expressed as$\dot V$O₂ [43.98 (1.70) vs 44.93 (2.39) ml - min⁻ - kg⁻], lactataemia [4.01 (0.28) vs 4.44 (0.37) mM - 1⁻], or heart rate [171 (3.36) vs 173 (3.11) min⁻]. In addition, strong correlations were noted between the two methods for$\dot V$O₂ (r=0.90,P<0.001), lactataemia (r=0.75,P<0.01), and heart rate (r=0.96,P<0.001). It is concluded that VT₂ coincides with LT₂ determination and that the ventilatory gas exchange method can thus satisfactorily evaluate the lactate accumulation threshold in young athletes.