[Does the choice of a reference system modify the analysis of ergospirometric values?].

The importance of the reference system (arbitrary abscissa units) for the analysis of the time courses of cardiopulmonary exercise test indices was assessed. Ten untrained students, 10 athletes, and 10 triathletes performed an exhaustion-limited cycling test. The courses of 20 pulmonary and hemodynamic indices were investigated with respect to the reference systems "heart rate," "relative and absolute oxygen consumption," "power," and a newly developed index "power-duration-product." Most of the significant differences were observed by reference to the power-duration-product. When using the power-duration-product as reference, the courses of eight indices differed significantly between students and triathletes, the courses of five indices between students and athletes, and the course of one index between athletes and triathletes. Since the number of the significant differences between the groups, as well as the courses themselves, depended clearly on the underlying reference system, the choice of the reference system must be considered as an important determinant for the analysis of cardiopulmonary exercise tests.