RESUMEN
The present study aimed to assess the capacity of stability and motor impact in the development of the balance of student athletes by reducing the support surface on the ball in the up plank position, by using three categories of balls of equal size, but with different elasticity and weight. In this study, the second aim was to investigate the differences in maintaining static balance, on different balls, between those who are practicing individual sports or team sports. The total study sample include 48 students, active athletes (45.8% of individual sports and 54.2% of team sports), age X ± SD 18.74 ± 1.94 years. The research included two test sessions (initial and final) applied in two stages. The static balance tests were performed by measuring the time maintaining the up plank position with two and three points of support on the three balls, with different characteristics of elasticity and ranges of deformation: medical ball, handball ball and fitness ball. The results of the study showed that the superior initial and final results were recorded on the fitness ball, and the inferior results on the medicine ball. The upper difference was recorded at the up plank position with two support points (arms, legs) on the fitness ball, at 4980 s, and the lowest in the same test on the medical ball, at 3420 s. The largest difference was recorded at the up plank position with three support points on the handball ball, at 7.082 s, and the lowest in the same test on the medical ball, at 3.093 s. The subjects of the study perceived that the most difficult position to execute was the up plank position on the medical ball with two support points, with 43.8%, and the easiest stability was registered in the up plank position on the fitness ball with three points of support, of 37.5%. The relevance of the research results from the possibility of using different balls in conditions of positioning and body posture with a diminished support base in order to improve physical fitness.