Study aim: To assess the intensities of three types of physical education (PE) classes corresponding to the phases of the teaching/learning process: Type 1--acquiring and developing skills, Type 2--selecting and applying skills, tactics and compositional principles and Type 3--evaluating and improving performance skills. Material and methods: A cohort of 350 schoolchildren, aged 13 years, from 3 selected urban schools in Poznan participated in the study. A total of 202 PE lessons was involved using heart rate (HR) monitors, one randomly selected subject per every class. Four intensity zones were assumed (less than 140, 140-159, 160-179, [greater than or equal to]180) and exercising time spent within each zone was measured. Results: Type 2 classes induced the most pronounced cardio-respiratory responses irrespectively of the kind of sport activities thus enhancing the cardio-respiratory fitness. Conclusions: Type 2 activities ought to be taken into consideration when designing PE curricula in order to avoid long runs of inadequate physiological stimuli. (Contains 5 tables.)