Test‐retest variability of VO(2max) using total‐capture indirect calorimetry reveals linear relationship of VO(2) and Power

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. VO(2) and VCO(2) 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) VO(2) level and −0.23 ± 0.80% (n = 31) at the 150 mL•min(−1) VCO(2) 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) VO(2) and VCO(2) ranges. Validation results for the Oxycon Pro in breath‐by‐breath mode were ‐ 2.2 ± 1.6% (n = 12) for VO(2) and 5.7 ± 3.3% (n = 12) for VCO(2) 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 VO(2) even with the highest range. VO(2max) was linear with the incline in P (max) over the full range.