IMPROVED FATIGUE RESISTANCE NOT ASSOCIATED WITH MAXIMUM OXYGEN-CONSUMPTION IN CREATINE-DEPLETED RATS

Effects of feeding of either creatine or its analog beta-guanidinoprop ionic acid (beta-GPA) on endurance work capacity and oxygen consumptio n were studied in rats. Resting high-energy phosphate contents in hind limb muscles were lower in the beta-GPA group and higher in the creati ne group than in controls. The glycogen contents in resting hindlimb m uscles of rats fed beta-GPA were significantly higher than those in co ntrols. The endurance run and swimming times to exhaustion were signif icantly greater (32-70%) in the beta-GPA group than in the control and creatine groups. However, there were no beneficial effects on the max imum oxygen consumption ((V) over dotO(2max)) and oxygen transport cap acity of blood by the feeding of beta-GPA. None of these parameters we re significantly influenced by creatine supply. Both maximum exercise time and (V) over dotO(2max) in the beta-GPA group were not changed by normalization of glycogen levels. The activities of mitochondrial enz ymes in skeletal muscles were higher in the beta-GPA group than in the controls. Thus endurance capacity is improved if the respiratory capa city of muscles is increased, even when the contents of high-energy ph osphates in muscles are lower. Increased endurance capacity was not di rectly associated with the elevated levels of muscle glycogen, oxygen transport capacity of blood, or (V) over dotO(2max).