The goal of this graduate thesis is to determine the level of physiological load on third-grade elementary school children after conducting fitness training. The research was made during Physical and Health Education class at Matija Vlačić Elementary School in Labin, involving 32 third-grade students, of whom 18 were boys and 14 were girls. This research examined three key variables - heart rate values at rest, heart rate values during the first round of exercise, and heart rate values during the second round of exercise. In order for the data to be as consistent as possible, the testing was conducted using ten different fitness training sessions. Each training session consisted of eight exercise tasks and was performed in a circular training setup. The process of performing the tasks was designed according to the arms-legs-back-abdomen scheme. The difficulty and complexity of these tests were adjusted to the abilities and capacities of students of that age. After carrying out the designed tests, it was determined that there is no statistically significant difference between genders in terms of physical fitness, thereby rejecting hypothesis number two. Observing the students' heart rates before performing the exercises and during the first and second rounds of exercise, we conclude that heart rates significantly increased during the second and third measurements compared to the initial measurement. However, the heart rate values during the first and second rounds of exercise were not high enough to meet the first hypothesis, which stated that the heart rate of each individual student would exceed 140 beats per minute. Therefore, hypothesis number one is also rejected. The third and the only hypothesis confirmed by this research refers to the differences in average heart rates between the first and second rounds of exercise, stating that the heart rates during the second round of exercise would be higher than those during the first round. This graduate thesis primarily aims to evaluate fitness or physical readiness of students at the age of ten, but we also learn about their psychological readiness. Considering today's mostly sedentary lifestyle, it is necessary to frequently monitor and check physical fitness of the children, in order to be able to provide the best possible feedback to affect the improvement of their health.