The aim of study was to investigate the effect of oral creatine supplementation upon muscle performance and aerobic capacity of the organism. Knee extensor muscles of two groups with 9 subjects in each were subjected to strength training with and without creatine supplementation (Cre and Pla) for 10 weeks, three times a week with an effort of up to 85% of maximal voluntary contraction (MVC). The Cre group received 5 g of creatine monohydrate a day. After 10 weeks strength training, an increase of MVC by 29 and 40% in training (isotonic) regimen was recorded for the Pla and Cre groups respectively. The muscle isokinetic torque increments of 10-11% were obtained in the Pla group at angular velocities corresponding to training velocities, and in the Cre group increments of 11-17% were recorded at all angular velocities tested. No changes were found in the fatigue test by the Pla group, whereas Cre group showed a tendency for an increase. The aerobic and anaerobic capacities of the organism did not decrease in both groups. Thus the creatine supplementation during strength training potentates an increase of force-velocity characteristics of trained muscle group without impeding aerobic capacity of the organism.