Test‐retest variability of VO _2max using total‐capture indirect calorimetry reveals linear relationship of VO ₂ and Power

Abstract

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.