The authors compare four variables of an attack jump between two groups of volleyball players, juniors and cadets. We observed during six months average strength of rebound, maximal impulse of strength, the time of whole rebound and the time reaching maximal impulse of strength. Th e group of juniors had better results for every parameter but cadets reached the highest improvement. Th e younger group gets to positive changes in average strength during rebound by 17,4 %, and for the time of whole rebound about 16,6 %. Maximal impulse of strength was increased by 3,9 % and the time reaching maximal impulse of strength was shorter 14,4 %. Juniors reached smaller changes than cadets, for average strength during rebound 9,2 %, maximal impulse of strength was increased by 12,5 % and the time of whole rebound about 10,6 %. Th e value of maximal impulse of strength was worst by 5,2 %. Th e both groups realized training programme of a very high quality, juniors 342 hours and cadets 211 hour of trainings load. Th e diff erences in results and value of changes are consequences of maturity, time of regular training process and performance level of our groups.