Reproducibility of Arterialized-Venous Blood Gas Samples at Moderate-, Heavy-, and Severe-Intensity Exercise

We assessed the day-to-day variability of arterialized-venous blood gas, electrolyte, and metabolite responses during cycling exercise within the moderate-, heavy-, and severe-intensity domains. We hypothesized that arterialized-venous blood variables would be consistent between-days at each exercise intensity. Fourteen healthy participants (mean ± SD [range], 55 ± 13 [36-75] years, [Formula: see text]O 2max = 34.1 ± 11.1 [16.2-49.7] mL·kg -1 ·min -1 ; 7 females) completed a maximal incremental cycling exercise protocol (Visit 1) and two step-incremental protocols (Visits 2 and 3) over three days. The step-incremental protocol involved three stages of exercise consisting of two 10-min stages, within the moderate- (MOD; 80% gas exchange threshold (GET)), and heavy-intensity domains (HVY; 70% between the GET and respiratory compensation point (RCP)) and a third stage within the severe-intensity domain (SVR; above RCP) until task disengagement. During MOD and HVY, 1.5 mL blood samples were withdrawn into heparinized syringes through a catheter placed in a heated hand vein at 5.0 and 7.5 minutes following stage onset and during the final minute of exercise in SVR. Blood samples were immediately analysed by a blood gas analyzer (ABL90Flex, Radiometer, Denmark). Two-way repeated measures ANOVA (intensity x day) and Pearson correlation coefficient (R) were used to assess between-day reproducibility at each intensity. Average power output for MOD, HVY, and SVR were 92±39 W, 130±50 W, and 169±74 W, respectively, eliciting steady-state [Formula: see text]O 2 of 1.54±0.57 L · min -1 , 1.99±0.73 L · min -1 , and peak [Formula: see text]O 2 of 2.46±1.00 L · min -1 . A significant main effect of intensity was found for all variables (p<0.05) but not for blood glucose ([Glu]; p=0.08). There was no main effect of day or intensity x day interaction for all variables. Combining all intensities, mean between-day changes were: pH: 0.01±0.02 (p=0.48, R=0.85); partial pressure of CO 2 : 0.4±2.3 mmHg (p=0.79, R=0.86);blood lactate concentration: 0.3±1.3 mmol . L -1 (p=0.25, R=0.92); [Glu]: 0.2±1.0 mmol . L -1 (p=0.64, R=0.17); bicarbonate concentration: -0.2±1.0 mmol . L -1 (p=0.32, R=0.90); potassium: 0.02±0.31 mmol . L -1 (p=0.57, R=0.83); sodium [Na + ]): 0.02±1.70 mmol . L -1 (p=0.91, R=0.78); calcium: 0.00±0.03 mmol . L -1 (p=0.23, R=0.57); and chloride: -0.66±2.62 mmol . L -1 (p=0.50, R=0.57). Arterialized-venous blood gas, electrolyte, and metabolite variables exhibited excellent test-retest reproducibility between-days. This was consistent irrespective of exercise intensity. Daniel A. Keir was supported by a NSERC Discovery Grant and the Canadian Foundation for Innovation. Robin Faricier was supported by an Ontario Graduate Scholarship. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.