Lactate vs. BE changes during cardiopulmonary exercise test

Background Lactate ( Lact ) in sports medicine, and arterial blood gas analysis ( BGA ) in cardiopulmonary exercise test ( CPET ) are established tools. Devices simultaneously measuring BGA and Lact are relatively expensive. Base excess ( BE ), routinely available from BGA, may provide equivalent information to lactate ( Lact ), during CPET. Research Question We asked if Lact can be replaced by BE during CPET. Method We assessed BE and Lact in a combined test, at rest, maximal exercise ( peak ) and 3 min post exercise ( 3p ) on a cycle ergometer. Out of 1715 diagnostic CPET investigations, 10 subjects with a complete dataset from each age group (20-29, 30-39, 40-49, 50-59, 60-69, 70-79, 80+yr) were randomly selected for analysis. Subjects with implausible results were excluded. The study was approved by the local Ethics Commission (2023). Results: Out of 70 subjects, 68 were included (f/m ratio 1.0, age 56±20 yr, height 170±9 cm, weight 76±17kg, BMI 26.1±5.1 kg/m 2 , peak VO2 19.7±8.6 mL/kg/min). The max and the 3p Lact levels were strongly correlated with the respective BE levels. Lactpeak=–0.61*BEpeak+3.15 (r=–0.71) and Lact3p=–0.64*BE3p+2.71 (r=–0.81) The lactate-increase from baseline to max ( ΔLactpeak ) was very strongly correlated to the respective BE-decrease ( ΔBEpeak ), and the same was true for the changes from baseline to 3p ( ΔLact3p vs. ΔBE3p , Figure 1 A and B). ΔLactpeak=–1.00*ΔBEpeak+0.85 (r=–0.91) and ΔLact3p=–0.87*ΔBE3p+0.58 (r=–0.94) The BE-decrease from peak to 3p was significantly increased vs. the respective Lact-increase (1.68±1.21 mmol/L vs. 0.77±0.82 mmol/L, p=8*10 -13 ) and this difference was significantly correlated with peak VO2 (r=-0.40; p=0.0009, Fig. 2). Conclusion During CPET, BE- and lactate-changes are strongly linearly correlated, and may be interchangeable. After exercise cessation, the disproportionate BE drop vs. the lactate increase likely reflects rapid re-oxygenation of the large venous blood pool. This suggests that this difference might be used as a measure of the dynamics of central venous oxygen saturation after exercise cessation and thus as a non-invasive measure of the utilization of the circulatory reserves (an unmet need). Publication History Article published online: 04 March 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany