Peak O2 consumption (V ̇ O 2 V̇O₂ peak) elicited by incremental exercise is considered the gold standard of cardiorespiratory fitness and a reliable predictor of mortality in humans 1. The measurement of V ̇ O 2 V̇O₂ peak requires a metabolic cart including sensible pieces of equipment, including flow sensors, O2/CO2 analyzers and moisture removal/drying systems, and large discrepancies in O2 consumption are observed within and between metabolic carts from distinct manufacturers. In contrast, peak power output (Wpeak) is easier to measure 2. A strong linear correlation between Wpeak and V ̇ O 2 V̇O₂ peak was observed in trained cyclists (r ≥ 0. 96, p 1. Peak power output (Wpeak) was defined as the highest workload maintained for at least 10 s during the incremental exercise test. Linear regression analyses (SPSS 26. 0, IBM) determined the relationship between Wpeak and V ̇ O 2 V̇O₂ peak in (i) all individuals, and (ii) subgroups according to binary variables (sex, age, V ̇ O 2 V̇O₂ peak). The true correlation was defined as the Pearson correlation coefficient (r) corrected for the measurement errors (reliabilities) of Wpeak and V ̇ O 2 V̇O₂ peak: true r = observed r ÷ (sqrt (reliability of Wpeak × reliability of V ̇ O 2 V̇O₂ peak) ). The reliabilities of Wpeak and V ̇ O 2 V̇O₂ peak were determined by the r of duplicate (test–retest) measurements performed in 10 study participants (50% ♀) within 2–7 days. The impact of sex, age and cardiorespiratory fitness (V ̇ O 2 V̇O₂ peak/kg) on the relationship between Wpeak and V ̇ O 2 V̇O₂ peak was assessed via the comparison of the regression line slopes in these subgroups: men vs. women, young vs. older, high vs. low V ̇ O 2 V̇O₂ peak/kg. Finally, the dependent sample t-test compared exercise economy (V ̇ O 2 V̇O₂ /W) at moderate and peak exercise intensities. The percentage difference between exercise economy (O2 consumption (V ̇ O 2 V̇O₂) /Watt (W) ) at moderate (100 W) and peak exercise intensities was determined to assess the anaerobic energy contribution to Wpeak. Wpeak and V ̇ O 2 V̇O₂ peak were linearly related (r = 0. 93, p < 0. 001) (Figure 1). The measurement errors (reliabilities) in Wpeak and VOpeak, as determined by the correlation of duplicate (test–retest) measurements, were r = 0. 99 and r = 0. 97, respectively. The true correlation between Wpeak and V ̇ O 2 V̇O₂ peak, i. e. , correcting for measurements errors in Wpeak and V ̇ O 2 V̇O₂ peak, approached a perfect linear relationship (r = 0. 95, p < 0. 001). The linear regression slopes did not differ according to sex (p = 0. 064), age (p = 0. 787) and V ̇ O 2 V̇O₂ peak/kg (p = 0. 539). The V ̇ O 2 V̇O₂ /W ratio was higher at moderate (100 W) compared with peak exercise intensities (12. 1 ± 2. 5 vs. 11. 6 ± 1. 6 mL·min−1·W−1, p < 0. 001). The percentage difference in V ̇ O 2 V̇O₂ /W between moderate and peak exercise intensities, reflecting the anaerobic energy percentage contribution to Wpeak, was 4. 5%. Age and cardiorespiratory fitness do not influence the relationship between Wpeak and V ̇ O 2 V̇O₂ peak, which contradicts typical assumptions in Exercise Physiology textbooks. How can aging and fitness status not modulate such a relationship? Their influence is indeed observed in studies measuring exercise efficiency on a treadmill 8. Instead, with cycle ergometry, neither sex, aging or fitness affect CEE 9. This divergence can be explained by the confounding biomechanical factors affecting running, but not cycling, exercise efficiency 10, and indicates that the ‘neat’ (metabolic) relationship between Wpeak and V ̇ O 2 V̇O₂ peak is robust to major moderating factors in humans. In conclusion, Wpeak and V ̇ O 2 V̇O₂ peak are statistically equivalent in healthy women and men and linearly correlated. Major potential moderating factors such as sex, age and cardiorespiratory fitness do not modify the relationship between Wpeak and V ̇ O 2 V̇O₂ peak. Furthermore, the relationship of O2 consumption and power output during incremental exercise denotes no relevant confounding influence of anaerobic energy production at peak effort. Collectively considered, large population studies can rely on incremental exercise Wpeak as a robust and accurate measure of cardiorespiratory fitness. Meihan Guo: investigation, writing – review and editing, formal analysis, supervision. David Montero: conceptualization, investigation, funding acquisition, writing – original draft, writing – review and editing, validation, methodology, formal analysis, supervision, data curation, resources. Xinyu Liu: investigation, formal analysis, supervision, writing – review and editing. Zihao Huang: investigation, writing – review and editing, formal analysis. Research Grant Council of Hong Kong (106210224 and 104006024, to D. M. ). The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request.
Liu et al. (Sun,) studied this question.