Normal values for cardiopulmonary exercise testing in children

In their recent paper Ten Harkel et al.1 presented new reference values for cardiopulmonary exercise testing in children. These data are urgently needed because systematic data for peak VO2 are outdated and data for the new variables are lacking altogether. In addition, the data show that there is a tremendous spread in exercise capacity in the current pediatric population with some being very fit and some “couch potatoes”. Old rules of thumb with a predicted reference range of 80–120% should no longer be used instead of a validated standard deviation. This has also been recently outlined in the reference value study on the treadmill providing percentiles2. To express the changes related to growth Ten Harkel et al. investigated the correlations with age. However, most of the developmental steps are linked to the onset or progress of puberty rather than to actual age. This is especially true for exercise capacity in boys. As the onset of puberty is also marked by increased growth, many pediatric developmental variables are correlating better with body height than with age. So I want to ask the authors to present the regression equations to age from their Table 3 again in the form of regression equations (with standard error and r) to body height.