L-tryptophan supplementation does not improve running performance

Plasma Amino Acids and Acylcarnitines Are Associated with the Female but Not Male Adolescent Swimmer's Performance: An Integration between Mass Spectrometry and Complex Network Approaches

The main aim of this study was to compare the performance over different distances, the critical velocity (CV), and plasma acylcarnitines/amino acids of male and female adolescent swimmers. Moreover, we applied the complex network approach to identify which molecules are associated with athletes' performances. On the first day under a controlled environment, blood samples were collected after 12 h of overnight fasting. Performance trials (100, 200, 400, and 800-m) were randomly performed in the subsequent four days in a swimming pool, and CV was determined by linear distance versus time mathematical function. Metabolomic analyses were carried out on a triple quadrupole mass spectrometer performing electrospray ionization in the positive ionization mode. No difference was observed between the performance of male and female swimmers. Except for 200-m distance (p = 0.08), plasma tyrosine was positively and significantly associated with the female times during the trials (100-m, p = 0.04; 400-m, p = 0.04; 800-m, p = 0.02), and inversely associated with the CV (p = 0.02). The complex network approach showed that glycine (0.406), glutamine (0.400), arginine (0.335), free carnitine (0.355), tryptophan (0.289), and histidine (0.271) were the most influential nodes to reach tyrosine. These results revealed a thread that must be explored in further randomized/controlled designs, improving the knowledge surrounding nutrition and the performance of adolescent swimmers.

The Importance of Quality Specifications in Safety Assessments of Amino Acids: The Cases of l-Tryptophan and l-Citrulline

The increasing consumption of amino acids from a wide variety of sources, including dietary supplements, natural health products, medical foods, infant formulas, athletic and work-out products, herbal medicines, and other national and international categories of nutritional and functional food products, increases the exposure to amino acids to amounts far beyond those normally obtained from the diet, thereby necessitating appropriate and robust safety assessments of these ingredients. Safety assessments of amino acids, similar to all food constituents, largely rely on the establishment of an upper limit [Tolerable Upper Intake Level (UL)] considered to be a guide for avoiding high intake, above which adverse or toxic effects might occur. However, reliable ULs have been difficult or impossible to define for amino acids because of inadequate toxicity studies in animals and scarce or missing clinical data, as well as a paucity or absence of adverse event reporting data. This review examines 2 amino acids that have been associated with in-market adverse events to show how quality specifications might have helped prevent the adverse clinical outcomes. We further highlight the importance of various factors that should be incorporated into an overall safety assessment of these and other amino acids. In addition to the traditional reliance on the established UL, well-defined quality specifications, review of synthesis and production strategies, potential interactions with drugs, contraindications with certain disease states, and cautionary use within certain age groups should all be taken into consideration.

L-Tryptophan: Biochemical, nutritional and pharmacological aspects

Tryptophan is important both for protein synthesis and as a precursor of niacin, serotonin and other metabolites. Tryptophan is an unusual amino acid because of the complexity of its metabolism, the variety and importance of its metabolites, the number and diversity of the diseases it is involved in, and because of its use in purified form as a pharmacological agent. This review covers the metabolism of tryptophan, its presence in the diet, the disorders associated with low tryptophan levels due to low dietary intake, malabsorption, or high rates of metabolism, the therapeutic effects of tryptophan and the side effects of tryptophan when it is used as a drug including eosinophilia myalgia syndrome.

Inhibition of tryptophan hydroxylase abolishes fatigue induced by central tryptophan in exercising rats

Fatigue during prolonged exercise is related to brain monoamines concentrations, but the mechanisms underlying this relationship have not been fully elucidated. We investigated the effects of increased central tryptophan (TRP) availability on physical performance and thermoregulation in running rats that were pretreated with parachlorophenylalanine (p-CPA), an inhibitor of the conversion of TRP to serotonin. On the 3 days before the experiment, adult male Wistar rats were treated with intraperitoneal (ip) injections of saline or p-CPA. On the day of the experiment, animals received intracerebroventricular (icv) injections of either saline or TRP (20.3 μM) and underwent a submaximal exercise test until fatigue. Icv TRP-treated rats that received ip saline presented higher heat storage rate and a 69% reduction in time to fatigue compared with the control animals. Pretreatment with ip p-CPA blocked the effects of TRP on thermoregulation and performance. Moreover, ip p-CPA administration accelerated cutaneous heat dissipation when compared with saline-pretreated rats. We conclude that an elevated availability of central TRP interferes with fatigue mechanisms of exercising rats. This response is modulated by serotonergic pathways, because TRP effects were blocked in the presence of p-CPA. Our data also support that a depletion of brain serotonin facilitates heat loss mechanisms during exercise.

Central fatigue: the serotonin hypothesis and beyond

The original central fatigue hypothesis suggested that an exercise-induced increase in extracellular serotonin concentrations in several brain regions contributed to the development of fatigue during prolonged exercise. Serotonin has been linked to fatigue because of its well known effects on sleep, lethargy and drowsiness and loss of motivation. Several nutritional and pharmacological studies have attempted to manipulate central serotonergic activity during exercise, but this work has yet to provide robust evidence for a significant role of serotonin in the fatigue process. However, it is important to note that brain function is not determined by a single neurotransmitter system and the interaction between brain serotonin and dopamine during prolonged exercise has also been explored as having a regulative role in the development of fatigue. This revised central fatigue hypothesis suggests that an increase in central ratio of serotonin to dopamine is associated with feelings of tiredness and lethargy, accelerating the onset of fatigue, whereas a low ratio favours improved performance through the maintenance of motivation and arousal. Convincing evidence for a role of dopamine in the development of fatigue comes from work investigating the physiological responses to amphetamine use, but other strategies to manipulate central catecholamines have yet to influence exercise capacity during exercise in temperate conditions. Recent findings have, however, provided support for a significant role of dopamine and noradrenaline (norepinephrine) in performance during exercise in the heat. As serotonergic and catecholaminergic projections innervate areas of the hypothalamus, the thermoregulatory centre, a change in the activity of these neurons may be expected to contribute to the control of body temperature whilst at rest and during exercise. Fatigue during prolonged exercise clearly is influenced by a complex interaction between peripheral and central factors.

A role for branched-chain amino acids in reducing central fatigue

Several factors have been identified to cause peripheral fatigue during exercise, whereas the mechanisms behind central fatigue are less well known. Changes in the brain 5-hydroxytryptamine (5-HT) level is one factor that has been suggested to cause fatigue. The rate-limiting step in the synthesis of 5-HT is the transport of tryptophan across the blood-brain barrier. This transport is influenced by the fraction of tryptophan available for transport into the brain and the concentration of the other large neutral amino acids, including the BCAAs (leucine, isoleucine, and valine), which are transported via the same carrier system. Studies in human subjects have shown that the plasma ratio of free tryptophan (unbound to albumin)/BCAAs increases and that tryptophan is taken up by the brain during endurance exercise, suggesting that this may increase the synthesis of 5-HT in the brain. Ingestion of BCAAs increases their concentration in plasma. This may reduce the uptake of tryptophan by the brain and also 5-HT synthesis and thereby delay fatigue. Accordingly, when BCAAs were supplied to human subjects during a standardized cycle ergometer exercise their ratings of perceived exertion and mental fatigue were reduced, and, during a competitive 30-km cross-country race, their performance on different cognitive tests was improved after the race. In some situations the intake of BCAAs also improves physical performance. The results also suggest that ingestion of carbohydrates during exercise delays a possible effect of BCAAs on fatigue since the brain's uptake of tryptophan is reduced.

Dietary supplements and sports performance: amino acids

This is the third in a series of six articles to discuss the major classes of dietary supplements (vitamins; minerals; amino acids; herbs or botanicals; metabolites, constituents/extracts, or combinations). The major focus is on efficacy of such dietary supplements to enhance exercise or sport performance.

Metabolic responses to oral tryptophan supplementation before exercise in horses

This study was conducted to evaluate the effects of oral tryptophan (Trp) supplementation on exercise capacity and metabolic responses in horses. Three horses had to perform an exercise test: a 15-min warm-up followed by a 60-min walk (1.7 m/s, W1), a 10-min trot (3.1 m/s, T1), a second 60-min walk (1.7 m/s, W2), a second 10-min trot (3.1 m/s, T2) and a final 30-min walk (1.7 m/s, W3) until the horses were unwilling to continue. The horses exercised on a treadmill at a 6% incline and with a constant draught load of 40 kg (0.44 kN). Two hours before exercise horses were given 50 g Trp (9.8-10.7 g Trp/100 kg BW) by nasogastric tube. A control exercise test was conducted without Trp. During the control test, one horse was able to finish the final 30-min walk (W3), whereas two horses finished W3 after Trp administration. Higher plasma Trp levels after Trp administration did not change significantly during exercise (Trp: start exercise, 524 +/- 41 micromol/l; end exercise 547 +/- 20 micromol/l; control: start exercise, 70 +/- 10 micromol/l; end exercise, 58 +/- 21 micromol/l). After Trp supplementation, blood lactate concentrations were significantly lower after the first and second trotting periods. Free fatty acids in plasma increased during exercise without any treatment-related differences. Although experimental plasma Trp levels were seven times higher than the control levels, Trp supplementation had no effect on exercise performance and metabolic responses to draught load exercise.

Interrelationship between physical activity and branched-chain amino acids

Some athletes can have quite high intakes of branched-chain amino acids (BCAAs) because of their high energy and protein intakes and also because they consume protein supplements, solutions of protein hydrolysates, and free amino acids. The requirement for protein may actually be higher in endurance athletes than in sedentary individuals because some amino acids, including the BCAAs, are oxidized in increased amounts during exercise compared with rest, and they must therefore be replenished by the diet. In the late 1970s, BCAAs were suggested to be the third fuel for skeletal muscle after carbohydrate and fat. However, the majority of later studies, using various exercise and treatment designs and several forms of administration of BCAAs (infusion, oral, and with and without carbohydrates), have failed to find a performance-enhancing effect. No valid scientific evidence supports the commercial claims that orally ingested BCAAs have an anticatabolic effect during and after exercise in humans or that BCAA supplements may accelerate the repair of muscle damage after exercise. The recommended protein intakes for athletes (1.2 to 1.8 g . kg body mass(-1) . d(-1)) do not seem to be harmful. Acute intakes of BCAA supplements of about 10-30 g/d seem to be without ill effect. However, the suggested reasons for taking such supplements have not received much support from well-controlled scientific studies.

Implicações do sistema serotoninérgico no exercício físico

Este trabalho revisa as alterações cerebrais de serotonina quando da oferta de nutrientes (carboidratos, proteínas e aminoácidos) durante atividade física. Utilizando a estratégia nutricional, o foco é o aminoácido precursor da serotonina cerebral: o triptofano; sendo um aminoácido essencial, é possível sua modulação via dieta. Uma abordagem emergente e polêmica está relacionada à fadiga durante atividade de curta e longa duração e sua relação com a função serotoninérgica cerebral. Os mecanismos propostos para o desenvolvimento de fadiga precoce durante o exercício se apresentam amplamente inexplorados. Assim serão discutidos os prováveis mecanismos envolvidos na "hipótese da fadiga central" e a oferta de carboidratos e aminoácidos como estratégia para retardar este fato durante atividade física e alcançar melhora no rendimento esportivo.

Cerebral perturbations provoked by prolonged exercise

This review addresses cerebral metabolic and neurohumoral alterations during prolonged exercise in humans with special focus on associations with fatigue. Global energy turnover in the brain is unaltered by the transition from rest to moderately intense exercise, apparently because exercise-induced activation of some brain regions including cortical motor areas is compensated for by reduced activity in other regions of the brain. However, strenuous exercise is associated with cerebral metabolic and neurohumoral alterations that may relate to central fatigue. Fatigue should be acknowledged as a complex phenomenon influenced by both peripheral and central factors. However, failure to drive the motorneurons adequately as a consequence of neurophysiological alterations seems to play a dominant role under some circumstances. During exercise with hyperthermia excessive accumulation of heat in the brain due to impeded heat removal by the cerebral circulation may elevate the brain temperature to >40 degrees C and impair the ability to sustain maximal motor activation. Also, when prolonged exercise results in hypoglycaemia, perceived exertion increases at the same time as the cerebral glucose uptake becomes low, and centrally mediated fatigue appears to arise as the cerebral energy turnover becomes restricted by the availability of substrates for the brain. Changes in serotonergic activity, inhibitory feed-back from the exercising muscles, elevated ammonia levels, and alterations in regional dopaminergic activity may also contribute to the impaired voluntary activation of the motorneurons after prolonged and strenuous exercise. Furthermore, central fatigue may involve depletion of cerebral glycogen stores, as signified by the observation that following exhaustive exercise the cerebral glucose uptake increases out of proportion to that of oxygen. In summary, prolonged exercise may induce homeostatic disturbances within the central nervous system (CNS) that subsequently attenuates motor activation. Therefore, strenuous exercise is a challenge not only to the cardiorespiratory and locomotive systems but also to the brain.

Evidence that tryptophan reduces mechanical efficiency and running performance in rats

It has been reported that exercise increases brain tryptophan (TRP), which is related to exhaustive fatigue. To study this further, the effect of increased TRP availability on the central nervous system (CNS) with regard to mechanical efficiency, oxygen consumption (VO(2)) and run-time to exhaustion was studied in normal untrained rats. Each rat was anesthetized with thiopental (30 mg/kg ip b. wt.) and fitted with a chronic guiding cannula attached to the right lateral cerebral ventricle 1 week prior to the experiments. Immediately before exercise, the rats were randomly injected through these cannulae with 2.0 microl of 0.15 M NaCl (n=6) or 20.3 microM L-TRP solution (n=6). Exercise consisted of running on a treadmill at 18 m min(-1) and 5% inclination until exhaustion. TRP-treated rats presented a decrease in their mechanical efficiency (21.25+/-0.84%, TRP group vs. 24.31+/-0.98%, saline-treated group; P< or =.05), and increased VO(2) at exhaustion (40.3+/-1.6 ml kg(-1) min(-1), TRP group vs. 36.0+/-0.8 ml kg(-1) min(-1), saline group; P< or =.05), indicating that the metabolic cost of exercise was higher in the former group. In addition, a highly significant reduction was also observed in run-time to exhaustion of TRP animals compared to those of the saline-treated group (15.2+/-1.52 min, TRP group vs. 50.6+/-5.4 min, saline group; P< or =.0001). It can be deduced from the data that intracerebroventricular TRP injection in rats increases O(2) consumption and reduces mechanical efficiency during exercise, diminishing running performance.

Facts and fallacies of purported ergogenic amino acid supplements

Although current research suggests that individuals involved in either high-intensity resistance or endurance exercise may have an increased need for dietary protein, the available research is either equivocal or negative relative to the ergogenic effects of supplementation with individual amino acids. Although some research suggests that the induction of hyperaminoacidemia via intravenous infusion of a balanced amino acid mixture may induce an increased muscle protein synthesis after exercise, no data support the finding that oral supplementation with amino acids, in contrast to dietary protein, as the source of amino acids is more effective. Some well-controlled studies suggest that aspartate salt supplementation may enhance endurance performance, but other studies do not, meriting additional research. Current data, including results for several well-controlled studies, indicated that supplementation with arginine, ornithine, or lysine, either separately or in combination, does not enhance the effect of exercise stimulation on either hGH or various measures of muscular strength or power in experienced weightlifters. Plasma levels of BCAA and tryptophan may play important roles in the cause of central fatigue during exercise, but the effects of BCAA or tryptophan supplementation do not seem to be effective ergogenics for endurance exercise performance, particularly when compared with carbohydrate supplementation, a more natural choice. Although glutamine supplementation may increase plasma glutamine levels, its effect on enhancement of the immune system and prevention of adverse effects of the overtraining syndrome are equivocal. Glycine, a precursor for creatine, does not seem to possess the ergogenic potential of creatine supplementation. Research with metabolic by-products of amino acid metabolism is in its infancy, and current research findings are equivocal relative to ergogenic applications. In general, physically active individuals are advised to obtain necessary amino acids through consumption of natural, high-quality protein foods.

Amino acid metabolism, branched-chain amino acid feeding and brain monoamine function

Although fatigue during prolonged exercise has traditionally been associated with peripheral factors relating to muscle metabolism, such as the depletion of muscle glycogen, more recent research has generated a renewed interest in amino acid metabolism per se and in the role of amino acids as precursors of brain neurotransmitter function. The concept of a 'central fatigue hypothesis' has done much to stimulate scientists to explore the functional role of the brain and CNS in the aetiology of the fatigue process. The concept has also generated a number of testable hypotheses by which it is possible to examine how the 'central' component of fatigue may act. The present review has attempted to bring together the current research in this area. There is good reason to believe that nutritional intervention may play an important role in relation to fatigue residing within the brain and CNS. Although an exciting possibility exists that nutritional manipulation may affect brain neurochemistry and ultimately sports performance, the experimental evidence to support this claim is, as yet, equivocal. A greater understanding of amino acid metabolism and, in particular, amino acid transport, will greatly improve future experimental designs used to test the efficacy of nutritional manipulation of amino acids and their effect on the central component of the fatigue process.

The effect of inhaled salbutamol and salmeterol on lung function and endurance performance in healthy well-trained athletes

The present randomized, double-blind placebo-controlled study aimed at investigating the possible improvement in endurance performance caused by inhaled salmeterol (long-acting beta 2-agonist) and salbutamol (short-acting) compared to placebo in 18 healthy well-trained athletes, aged 17-30 years old. Lung function (flow-volume loops) was measured before and after each inhaled study drug and after run to exhaustion. After inhalation of study drug and 10 min warm-up, anaerobic threshold was measured; thereafter maximum oxygen uptake, peak ventilation and running time until exhaustion during a brief graded exercise were measured. No significant differences were found for ventilation, oxygen uptake or heart rate at anaerobic threshold or at maximum performance between placebo and the beta 2-agonists. Lung function increased significantly after exercise, but without differences between the beta 2-agonists and placebo. Running time till exhaustion was significantly reduced after both the long- and the short-acting beta 2-agonist compared to the placebo.

Exercise and brain neurotransmission

Physical exercise influences the central dopaminergic, noradrenergic and serotonergic systems. A number of studies have examined brain noradrenaline (norepinephrine), serotonin (5-hydroxytryptamine; 5-HT) and dopamine with exercise. Although there are great discrepancies in experimental protocols, the results indicate that there is evidence in favour of changes in synthesis and metabolism of monoamines during exercise. There is a possibility that the interactions between brain neurotransmitters and their specific receptors could play a role in the onset of fatigue during prolonged exercise. The data on the effects of branched chain amino acid (BCAA) supplementation and 'central fatigue' seem to be conflicting, although recent studies suggest that BCAA supplementation has no influence on endurance performance. There are numerous levels at which central neurotransmitters can affect motor behaviour; from sensory perception, and sensory-motor integration, to motor effector mechanisms. However, the crucial point is whether or not the changes in neurotransmitter levels trigger or reflect changes in monoamine release. Until recently most studies were done on homogenised tissue, which gives no indication of the dynamic release of neurotransmitters in the extracellular space of living organisms. Recently, new techniques such as microdialysis are voltammetry were introduced to measure in vivo release of neurotransmitters. Microdialysis can collect virtually any substance from the brain of a freely moving animal with a limited amount of tissue trauma. This method allows measurement of local neurotransmitter release during on-going behavioural changes such as exercise. The results of the first studies using these methods indicate that the release of most neurotransmitters is influenced by exercise. Although the few studies that have been published to date show some discrepancies, we feel that these recently developed and more sophisticated in vivo methods will improve our insight into the relationship between the monoamine and other transmitters during exercise. Continued quantitative and qualitative research needs to be conducted so that a further understanding of the effects of exercise on brain neurotransmission can be gained.