Progress Update and Challenges on [Formula: see text] O(2max) Testing and Interpretation

The maximal oxygen uptake ([Formula: see text] 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 [Formula: see text] 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 [Formula: see text] O(2max) from the breath-by-breath data can change the [Formula: see text] 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 [Formula: see text] 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 [Formula: see text] O(2max) and identifying the plateau. In training studies, clinical interventions and meta-analysis, reporting of [Formula: see text] 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 [Formula: see text] O(2max) to similar averaging strategies. A lack of improvement of [Formula: see text] 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 [Formula: see text] O(2max).