In the mid- and eastern European countries a trend of life-style deterioration is described, following with several years delay of a similar trend in the western European countries. In relation to high energy intake from imbalanced diet and insufficient physical activity, the children tend to elevated ratios of overweight and obese individuals. Obesity negatively influences performance, as well as the amount of physical activity has an impact on performance (in sense of aerobic capacity) of the individual. We analyzed the data of children (participants of the ELSPAC study) at the ages of 11, 13 and 15 years of age with the aim of finding out whether an association between the amount of physical activity and performance exists of children in Brno (Czech Republic). The amount of physical activity was evaluated from self-reported hours of exercise, performance was assessed via a step-up test (at the age of 11 and 13) and via W170 ergometric test (at the age of 15). The obtained results do not show a trend towards a significant decrease in physical activity and performance of children from Brno. An association (although it appears to be quite weak) between the amount of physical activity and performance in Czech children was found.