The power-duration product--evaluation of a new reference system for cardiopulmonary exercise testing

The aim of this study was to assess the discriminatory power of the new reference system, power-duration product (PDP), for the analysis of haemodynamic and metabolic variables derived from cardiopulmonary exercise tests. The PDP was calculated as the cumulative index of the product of power (W) times the duration (minutes) of each individual exercise step. The study comprised 30 healthy male volunteers, who were classified into three groups with respect to their regular physical activity: 10 untrained medical students (students), 10 sprinters and long-jumpers (athletes) and 10 endurance athletes performing triathlon (triathletes). Twenty metabolic and haemodynamic variables were recorded throughout exhaustion-limited cycling ergometry. The data were analysed with respect to five reference systems (heart rate, relative and absolute oxygen consumption/body surface area, power, and PDP). A total of 14 differences between modified time courses of haemodynamic and metabolic variables in the three groups of volunteers were observed by reference to PDP, 12 by reference to relative oxygen consumption/body surface area, 11 by reference to heart rate, 8 by reference to absolute oxygen consumption/body surface area, and 7 by reference to power. When using PDP as the reference, the time courses of 8 parameters differed significantly between students and triathletes, 5 between students and athletes, and 1 between athletes and triathletes. In addition to its discriminatory superiority for the comparison of different groups characterized by different cardiopulmonary training and endurance, it was found that PDP permitted a better characterization of the individually performed exercise than the consideration of power per se.