Test-retest variability of VO_2max using total-capture indirect calorimetry reveals linear relationship of VO₂ and...

This study aimed to analyze the intra-individual variation in VO_2max of human subjects using total-capture and free-flow indirect calorimetry. Twenty-seven men (27 ± 5 year; VO_2max 49-79 mL•kg^-1 •min^-1 ) performed two maximal exertion tests (CPETs) on a cycle ergometer, separated by a 7 ± 2 day interval. VO₂ and VCO₂ were assessed using an indirect calorimeter (Omnical) with total capture of exhalation in a free-flow airstream. Thirteen subjects performed a third maximal exertion test using a breath-by-breath calorimeter (Oxycon Pro). On-site validation was deemed a requirement. For the Omnical, the mean within-subject CV for VO_2max was 1.2 ± 0.9% (0.0%-4.4%) and for ergometer workload P _max 1.3 ± 1.3% (0%-4.6%). VO_2max values with the Oxycon Pro were significantly lower in comparison with Omnical (P < 0.001; t test) with mean 3570 vs 4061 and difference SD 361 mL•min^-1 . Validation results for the Omnical with methanol combustion were -0.05 ± 0.70% (mean ± SD; n = 31) at the 225 mL•min^-1 VO₂ level and -0.23 ± 0.80% (n = 31) at the 150 mL•min^-1 VCO₂ level. Results using gas infusion were 0.04 ± 0.75% (n = 34) and -0.99 ± 1.05% (n = 24) over the respective 500-6000 mL•min^-1 VO₂ and VCO₂ ranges. Validation results for the Oxycon Pro in breath-by-breath mode were - 2.2 ± 1.6% (n = 12) for VO₂ and 5.7 ± 3.3% (n = 12) for VCO₂ over the 1000-4000 mL•min^-1 range. On a Visual analog scale, participants reported improved breathing using the free-flow indirect calorimetry (score 7.6 ± 1.2 vs 5.1 ± 2.7, P = 0.008). We conclude that total capturing free-flow indirect calorimetry is suitable for measuring VO₂ even with the highest range. VO_2max was linear with the incline in P _max over the full range.