Progress Update and Challenges on V . O2max Testing and Interpretation

Abstract

The maximal oxygen uptake ( $\stackrel{.}{\text{V}}$ O_2max) is the primary determinant of endurance performance in heterogeneous populations and has predictive value for clinical outcomes and all-cause mortality. Accurate and precise measurement of $\stackrel{.}{\text{V}}$ O_2max requires the adherence to quality control procedures, including combustion testing and the use of standardized incremental exercise protocols with a verification phase preceded by an adequate familiarization. The data averaging strategy employed to calculate the $\stackrel{.}{\text{V}}$ O_2max from the breath-by-breath data can change the $\stackrel{.}{\text{V}}$ O_2max value by 4-10%. The lower the number of breaths or smaller the number of seconds included in the averaging block, the higher the calculated $\stackrel{.}{\text{V}}$ O_2max value with this effect being more prominent in untrained subjects. Smaller averaging strategies in number of breaths or seconds (less than 30 breaths or seconds) facilitate the identification of the plateau phenomenon without reducing the reliability of the measurements. When employing metabolic carts, averaging intervals including 15-20 breaths or seconds are preferable as a compromise between capturing the true $\stackrel{.}{\text{V}}$ O_2max and identifying the plateau. In training studies, clinical interventions and meta-analysis, reporting of $\stackrel{.}{\text{V}}$ O_2max in absolute values and inclusion of protocols and the averaging strategies arise as imperative to permit adequate comparisons. Newly developed correction equations can be used to normalize $\stackrel{.}{\text{V}}$ O_2max to similar averaging strategies. A lack of improvement of $\stackrel{.}{\text{V}}$ O_2max with training does not mean that the training program has elicited no adaptations, since peak cardiac output and mitochondrial oxidative capacity may be increased without changes in $\stackrel{.}{\text{V}}$ O_2max.

Keywords: breath-by-breath; calibration; cardiopulmonary exercise testing; indirect calorimetry; metabolic cart; performance; ramp exercise; reproducibility.

FIGURE 1

Change in the $\stackrel{.}{\text{V}}$O_2max value and its reproducibility in subjects divergent for fitness status using two different automated metabolic carts operated in breath-by-breath mode with different rolling breath-averages. (A) $\stackrel{.}{\text{V}}$O_2max response in a heterogeneous group of sedentary and physically active overweight and obese subjects ($\stackrel{.}{\text{V}}$O_2max range: 13–40 mL/kg/min) assessed with Vmax N29 Sensormedics (n = 51). (B) $\stackrel{.}{\text{V}}$O_2max response in a group of endurance-trained subjects ($\stackrel{.}{\text{V}}$O_2max range: 40–60 mL/kg/min) assessed with Vyntus CPX (n = 11). (C) $\stackrel{.}{\text{V}}$O_2max response in a group of recreationally active and endurance-trained subjects ($\stackrel{.}{\text{V}}$O_2max range: 35–60 mL/kg/min) performing one test with Vmax N29 and a duplicate test with Vyntus CPX in random order (n = 11). (D) $\stackrel{.}{\text{V}}$O_2max response assessed with the Vmax N29 and Vyntus metabolic carts in two groups of nine subjects each of similar $\stackrel{.}{\text{V}}$O_2max ($\stackrel{.}{\text{V}}$O_2max range: 40–60 mL/kg/min) (B). CV_f (%), coefficient of variation calculated as proposed by Forkman (2009). Note the clear trend for lower reproducibility and a larger decay of the $\stackrel{.}{\text{V}}$O_2max the lower the fitness of the subjects. Modified from Martin-Rincon et al. (2019) with kind permission.

FIGURE 2

Representative $\stackrel{.}{\text{V}}$O₂ data during an incremental exercise to exhaustion in one demonstrative subject using different averaging blocks (breaths and seconds). Calculation of averaging blocks for the breath-based strategy refers to a “rolling” breath average, while time-based data were stationary time-averaged, both with the corresponding length of the block (e.g., 10 breaths or 10 s). Data are presented as (A) raw breath-by-breath, (B) 15 breaths and 15 s, (C) 30 breaths and 30 s, (D) 60 breaths and 60 s. Note the slightly higher values of breath-based averages compared to time-based averages of the same number, although a high concordance (concordance correlation coefficient = CCC > 0.97) is present. Modified from Martin-Rincon et al. (2019) with kind permission.