Metabolic adaptation to daily exercise of moderate intensity to exhaustion in the rat

Summary

The rats were made to run daily to exhaustion, for 28 days at a speed of 1,200 m·h⁻¹ on a treadmill set at a gradient of + 10°. The training increased the time of running to exhaustion [184 (SD 49) and 308 (SD 28) min on the 1st and 28th day, respectively; P<0.001]. The body mass was reduced by training [257 (SD 21) g before and 221 (SD 20) g after; P<0.001] whereas the food intake increased [9 (SD 1) g·100 g⁻ body mass before and 14 (SD 2) g after; P0.001]. The heart mass was not affected by training. Training increased the resting glycogen concentration in muscles composed of different fibre types (soleus, white and red vastus muscles) and in the liver, but had no effect on its concentration in the heart and diaphragm. During exercise lasting for 30 min glycogen mobilization in the red vastus and soleus muscles and the liver was more pronounced after than before training. A “sparing” effect of training on the skeletal muscles and liver glycogen was markedly apparent only after exericse to exhaustion. The trained rats, contrary to the untrained, did not develop hypoglycaemia during exercise to exhaustion. An increase in the plasma free fatty acid concentration during exercise after training was delayed and attenuated compared to that before training. The 24-h excretion of urea after exercise to exhaustion on the 28th day of training was higher than on the 1st day by 39% (P<0.001). It is concluded that metabolic adaptation to training consisting of daily bouts of exercise to exhaustion differs in many aspects from that so far described for other endurance training protocols.