Administration of a GABA(B) agonist baclofen before running to exhaustion in the rat: Effects on performance and on some indicators of fatigue

The present study was designed to examine the effects of administration of a GABAergic agonist (Baclofen) on run-time to exhaustion in trained and untrained rats, and on some indicators of fatigue. Run-time to exhaustion on a treadmill set at a speed of 25 m . min(-1) was significantly increased in both untrained (p < 0.01) and trained rats (p < 0.005) administered with baclofen one hour before the exercise. The animals who had run the longest time displayed the lowest concentrations of liver and muscle glycogen, and a decrease in plasma glucose concentrations (p < 0.05). The results of this investigation suggest that fatigue during prolonged exercise can be influenced by pharmacological administration of a GABAergic agonist. Indicators of fatigue such as glycemia, liver and muscular glycogen are not the limiting factors of performance and central mechanisms play a key role at exhaustion.