Abstract
BackgroundThe present study examined putative modulators and indices of brain serotonergic and dopaminergic function, perceptual responses, and endurance exercise performance following caffeine co-ingested with a high fat meal.MethodsTrained humans (n = 10) performed three constant-load cycling tests at 73% of maximal oxygen uptake (VO2max) until exhaustion at 10°C remove space throughout. Prior to the first test, subjects consumed a 90% carbohydrate meal (Control trial) and for the remaining two tests, a 90% fat meal with (FC trial) and without (F trial) caffeine.ResultsTime to exhaustion was not different between the F and FC trials (P > 0.05); [Control trial: 116(88-145) min; F trial: 122(96-144) min; FC trial: 127(107-176) min]. However, leg muscular discomfort during exercise was significantly lower on the FC relative to F trial (P < 0.01). There were no significant differences between F and FC trials in key modulators and indices of brain serotonergic (5-HT) and dopaminergic (DA) function [(i.e. plasma free and total tryptophan (Trp), tyrosine (Tyr), large neutral amino acids (LNAA), Trp:LNAA ratio, free-Trp:Tyr ratio, total Trp:Tyr ratio, and plasma prolactin] (P > 0.05) with the exception of plasma free-Trp:LNAA ratio which was higher at 90 min and at exhaustion during the FC trial (P < 0.05).ConclusionsNeither brain 5-HT nor DA systems would appear to be implicated in the fatigue process when exercise is performed without significant thermoregulatory stress, thus indicating fatigue development during exercise in relatively cold temperatures to occur predominantly due to glycogen depletion.
Highlights
Newsholme et al [15] proposed that an increase in activity of 5-HT neurons in various brain regions such as the midbrain and hypothalamus may contribute to fatigue development during prolonged exercise, a mechanism commonly referred as the "central fatigue hypothesis". 5-HT is synthesised from the essential amino acid precursor tryptophan (Trp) and during periods of high 5HT activity, the rate of 5-HT synthesis can be influenced by the uptake of Trp from plasma [16]
Prolactin and blood metabolites There were no significant differences between F and FC trials in total [Trp], [Tyr], [LNAA], total [Trp]:[LNAA] ratio and total [Trp]:[Tyr] ratio (Table 2)
The present study examined the relationship between the putative modulators and indices of brain serotonergic and dopaminergic function, effort perception and endurance exercise performance in a relatively cold (10°C) environment following caffeine co-ingestion with a high fat meal in well-trained humans
Summary
The present study examined putative modulators and indices of brain serotonergic and dopaminergic function, perceptual responses, and endurance exercise performance following caffeine co-ingested with a high fat meal. One plausible explanation for the reduced effort perception observed following caffeine ingestion [12] may be due to the increased brain DA levels [8] and/or to the reduced brain 5-HT response [10] This is consistent with the hypothesis that a high brain 5-HT:DA ratio may favour increased subjective effort and central fatigue, while a low 5-HT:DA ratio may favour increased arousal and central motivation [13,14]. The aim of the present study was to examine the relationship between peripheral modulators of brain 5-HT and DA function, perceptual responses and endurance performance during prolonged submaximal exercise to volitional fatigue, following caffeine co-ingested with a high fat meal in well-trained cyclists. The pre-exercise high fat meal was employed to imitate physiologically the metabolic effects of caffeine in an attempt to distinguish between the potential peripheral and/or central effects of caffeine
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