Background:
This study aims to analyse the relationship between physical activity (PA) and body mass index (BMI) in undergraduate university students of three fields of study from the four Visegrad Group countries – Slovakia, the Czech Republic, Poland, and Hungary.

Material and methods:
The research was conducted in 2015 on adolescent undergraduate university student populations in three fields of study – humanities, medical, and technical sciences. The sample included 2,484 students in total. The data was collected using the extended version of the standardised International Physical Activity Questionnaire (IPAQ). Students completed the questionnaire in class via the INDARES online system.

Results:
The results confirmed significant differences in PA between sexes in favour of boys both in its overall manifestation and in the individual levels of PA intensity (p<0.05). The comparison of the four countries revealed significant differences in PA in boys and girls in all PA domains (p<0.05). The evaluation of the total BMI, as well as the one measured in individual countries confirmed a significant difference between sexes in favour of boys (p<0.05). The study of the relationship between PA and BMI did not reveal a statistically significant dependence in any of the tested domains. This conclusion applies both to boys and girls.

Conclusions:
Boys are generally more physically active than girls overall and in individual fields of study. This finding is valid for all the studied countries. Also, boys exhibit higher BMI in all the studied categories. No significant relation between PA intensity and volume and BMI was found in either sex.