Time trial performance in normal and high ambient temperature: is there a role for 5-HT?

Abstract

The original central fatigue hypothesis suggested that fatigue during prolonged exercise might be due to higher 5-HT activity. Therefore, we examined the effects of acute administration of a selective 5-HT reuptake inhibitor (SSRI) on performance and thermoregulation. Eleven healthy trained male cyclists completed four experimental trials (two in 18 degrees C, two in 30 degrees C) in a double-blind randomised crossover design. Subjects ingested either a placebo (PLA: lactose 2 x 10 mg) or citalopram (CITAL 2 x 10 mg) on the evening before and the morning of the trial. Subjects cycled for 60 min at 55% W(max), immediately followed by a time trial (TT) to measure performance. The significance level was set at P < 0.05. Acute SSRI did not significantly change performance on the TT (18 degrees C P = 0.518; 30 degrees C P = 0.112). During recovery at 30 degrees C, core temperature was significantly lower in the CITAL trial (P < 0.012). At 30 degrees C heart rate was significantly lower after exercise in CITAL (P = 0.013). CITAL significantly increased cortisol concentrations at rest (P = 0.016), after the TT (P = 0.006) and after 15-min recovery (P = 0.041) at 30 degrees C. 5-HT reuptake inhibition did not cause significant reductions in performance. Core temperature was significantly lower only after the time trial in heat after CITAL administration. The present work failed to prove whether or not 5-HT has an exclusive role in the onset of centrally mediated fatigue during prolonged exercise in both normal and high ambient temperature.

Role of Central Fatigue in Resistance and Endurance Exercises: An Emphasis on Mechanisms and Potential Sites

“…Some studies Wilson & Maughan, 1992) diagnosed reduced performance after administration of paroxetine and fluoxetine (reuptake inhibitors of 5-HT). However, most studies (Pannier, Bouckaert, & Lefebvre, 1995;Parise, Bosman, Boecker, Barry, & Tarnopolssky, 2001;Roelands et al, 2009) couldn't confirm these findings. Strüder and Weicker (2001) suggested the reduced performance capacity occurred after acute administration of 5-HT reuptake inhibitors may be as a result of the reduced functional capacity of 5-HT as a multipurpose generator that provides adaptability of neural network to address the needs of the central critical demands, not because of the increased activity of 5-HT.…”

“…Furthermore, microinjection of apomorphine (an agonist of DA) into the hypothalamus of rat creates a DA mediated fall of temperature (Brown, Gisolf, & Mora, 1982). Besides, DA release in PO/AH during the treadmill exercise was risen , and DA caused to the increased temperature of the rats body (Myers & Yaksh, 1968), It can be expected that changes in the concentration of these neurotransmitters, helps to the changes in temperature regulation because of fatigue, especially when the exercise is being done in the hot environment (Roelands et al, 2009).…”

The Involvement of Brain Monoamines in the Onset of Hyperthermic Central Fatigue

“…During exercise, the acute ingestion of the drug in humans has been shown to improve time-trial exercise performance in a warm environment, despite higher body temperatures (Watson et al, 2005). In contrast to acute bupropion administration, the chronic ingestion of the drug does not influence time-trial exercise performance under the same environmental conditions, aside from inducing lower body temperature values than the temperatures observed during the acute bupropion study (Roelands et al, 2009;Watson et al, 2005). The mechanism for these observed discrepancies in bupropion administration seems to be the possible adaptation of central neurotransmitter homeostases during the treatment (Roelands et al, 2009).…”

“…The data led to the hypothesis that elevated serotonin content may contribute to poor exercise performance during periods of excessive training. A special focus has been given to the pharmacological manipulations used to elucidate the relationship between increased serotonergic activity and the early onset of fatigue (Bailey et al, 1993;Roelands et al, 2009). A study by Bailey et al (1993) demonstrated that exercise performance benefitted from the use of a serotonin antagonist, while treatment with a serotonin agonist led to a detriment in exercise performance.…”

“…However, the results are contradictory and inconclusive. Although data have demonstrated no effect of different serotonin reuptake inhibitors (pizotifen, fluoxetine, citalopam) on exercise performance in humans (Meeusen et al, 2001;Pannier et al, 1995;Parise et al, 2001;Roelands et al, 2009;Strachan et al, 2004), findings from Struder et al (1998) and W. M. Wilson et al (1992) indicate that fatigue occurs sooner with pharmacological augmentation of the brain's serotonergic activity by serotonin re-uptake inhibitor (paroxetine) supplements. These different outcomes might be explained by divergent exercise protocols, pharmacological manipulations, drug receptor specificity and drug dosages.…”