Improved fatigue resistance not associated with maximum oxygen consumption in creatine-depleted rats

Tanaka, T., Y. Ohira, M. Danda, H. Hatta, and I. Nishi.Improved fatigue resistance not associated with maximum oxygen consumption in creatine-depleted rats. J. Appl. Physiol.82 (6): 1911–1917, 1997.—Effects of feeding of either creatine or its analog β-guanidinopropionic acid (β-GPA) on endurance work capacity and oxygen consumption were studied in rats. Resting high-energy phosphate contents in hindlimb muscles were lower in the β-GPA group and higher in the creatine group than in controls. The glycogen contents in resting hindlimb muscles of rats fed β-GPA were significantly higher than those in controls. The endurance run and swimming times to exhaustion were significantly greater (32–70%) in the β-GPA group than in the control and creatine groups. However, there were no beneficial effects on the maximum oxygen consumption (V˙o2 max) and oxygen transport capacity of blood by the feeding of β-GPA. None of these parameters were significantly influenced by creatine supply. Both maximum exercise time andV˙o2 maxin the β-GPA group were not changed by normalization of glycogen levels. The activities of mitochondrial enzymes in skeletal muscles were higher in the β-GPA group than in the controls. Thus endurance capacity is improved if the respiratory capacity of muscles is increased, even when the contents of high-energy phosphates in muscles are lower. Increased endurance capacity was not directly associated with the elevated levels of muscle glycogen, oxygen transport capacity of blood, orV˙o2 max.