Introduction: The central fatigue hypothesis is based on the assumption that during prolonged exercise the synthesis and metabolism of central monoamines, in particular serotonin (5-HT), dopamine (DA) and noradrenaline (NA), are influenced (Meeusen,2006). It is not known however which neurotransmitter system is responsible for accelerating or delaying the onset of fatigue during prolonged exercise. The influence of ambient temperature on fatigue is well studied, but there are little available data on the combined effects of pharmacological manipulations and environmental heat stress on performance. Therefore, the effects of acute administration of individual 5-HT, DA and NA reuptake inhibitors (5-HTRI, DARI, NARI) on performance and thermoregulation were examined in normal and high ambient temperature. Methods: In three separate studies, between 8 and 11 healthy trained male cyclists completed four experimental trials (two in 18°C, two in 30°C) in a double blind-randomized crossover design. Subjects ingested either a placebo or drug (Citalopram - 5-HTRI, Reboxetine - NARI, Ritalin - DARI) on the morning of the trial. Subjects cycled for 60 min at 55%Wmax, immediately followed by a time trial to measure performance. Tcore, skin temperature, heart rate, blood pressure, sweat loss, RPE, thermal stress, blood lactate and hormonal data were recorded. The significance level was set at p<.05. Results: 5-HTRI did not induce any significant change in performance in 18 and 30°C (p=0.518; p=0.112; Roelands,2009). DARI improved performance in high ambient temperature with more than 7min (p=0.049; Roelands, 2008a). Core temperatures rose significantly higher compared to placebo (p=0.05) while no changes in RPE and thermal stress were found. NARI decreased performance by 3min in 18°C and 8min in 30°C (p=0.018;p=0.007; Roelands,2008b). Discussion/Conclusion 5HTRI did not cause a change in exercise capacity, thereby confirming other studies (Meeusen,2001; Strachan,2004;2005) and indicating that the role of 5-HT in the onset of fatigue during prolonged exercise is limited in humans. It appears that DA neurotransmission is capable of increasing motivation and drive to continue exercising, even at very high core temperatures, without changing the subjects` perception of effort and internal temperature. Manipulation of NA neurotransmission, in contrast, has negative effects on performance. In conclusion, most probably central fatigue is caused by a complex interplay between the different neurotransmitters systems, with the most important role for the catecholamines DA and NA on either side of the performance spectrum.
© Copyright 2009 14th annual Congress of the European College of Sport Science, Oslo/Norway, June 24-27, 2009, Book of Abstracts. Veröffentlicht von The Norwegian School of Sport Sciences. Alle Rechte vorbehalten.