EFFECTS OF CAFFEINE ON TIME TO EXHAUSTION IN EXERCISE PERFORMED BELOWAND ABOVE THE ANAEROBIC THRESHOLD

Controversy still exists concerning the potential ergogenic benefit of caffeine (CAF) for exercise performance. The put-pose of this study w as to compare the effects of CAF ingestion on endurance performance du ring exercise on a bicycle ergometer at two different intensities, i.e ., approximately 10% below and 10% above the anaerobic threshold (AT). Eight untrained males, non-regular consumers of CAF, participated in this study. AT, defined as the intensity (watts) corresponding to a la ctate concentration of 4 mM, was determined during an incremental exer cise test from rest to exhaustion on an electrically braked cycle ergo meter. On the basis of these measurements, the subjects were asked to cycle until exhaustion at two different intensities, i.e., approximate ly 10% below and 10% above AT. Each intensity was performed twice in a double-blind randomized order by ingesting either CAF (5 mg/kg) or a placebo (PLA) 60 min prior to the test. Venous blood was analyzed for free fatty acid, glucose, and lactate, before, during, and immediately after exercise. Rating of perceived exertion and time to exhaustion w ere also measured during each trial. There were no differences in free fatty acids or lactate levels between CAF and PLA during and immediat ely after exercise for either intensity. Immediately after exercise gl ucose increased in the CAF trial at both intensities. Rating of percei ved exertion was significantly lower (CAF = 14.1 +/- 2.5 vs PLA = 16.6 +/- 2.4) and time to exhaustion was significantly higher (CAF = 46.54 +/- 8.05 min vs PLA = 32.42 +/- 14.81 min) during exercise below AT w ith CAF. However, there was no effect of CAF treatment on rating of pe rceived exertion (CAF = 18.0 +/- 2.7 vs PL,4 = 17.6 +/- 2.3) and time to exhaustion (CAF = 18.45 +/- 7.28 min vs PLA = 19.17 +/- 4.37 min) d uring exercise above AT. We conclude that in untrained subjects caffei ne can improve endurance performance during prolonged exercise perform ed below AT and that the decrease of perceived exertion can be involve d in this process.