Study aim: To assess the relations between anthropometric and cardio-respiratory indices, and aerobic capacity of students, differing in the level of physical activity, under resting and exercise conditions.Material and methods: A group of 87 male and 75 female students volunteered to participate in the study. Their physical activity was evaluated by Seven-Day Physical Activity Recall questionnaire. Anthropometric (body height and mass, body fat content, BMI and WHR) and physiological indices (heart rate, blood pressure, O2max, CO2 and minute ventilation) were recorded. Body fat content was determined using a BIA device; respiratory data were recorded in a cycle ergometer test. The subjects were classified by their O2max values into ‘high’ or ‘low’ categories, the cut-off values of lower and upper quartiles serving as criteria.Results: Male and female students expended 10.2 ± 4.6 and 8.4 ± 5.3 kcal/kg/day, respectively, the O2max amounting to 48.4 ± 6.4 and 41.1 ± 4.7 ml/kg/min, respectively. Subjects having high O2max had significantly higher energy expenditure on physical activities, fat-free mass, body water content and maximal ventilation, and lower body mass, BMI, body fat content, resting heart rate and diastolic pressure.Conclusions: When investigating into the relationships between physical activity and physiological features, the latter ought to be related to O2max rather than to energy expenditure which may depend on other than physiological variables.