Abstract
BackgroundSince the 1980s the role of tryptophan in modulating fatigue has been the subject of debate. According to some models, tryptophan delays the onset of fatigue. Conversely, in other models, this amino acid is implicated in generating fatigue. This study attempts to shed some light on the debate. MethodTen elite (non-professional) road racing cyclists took part in a double-blind study employing paired data under standardised dietary and training conditions. Each volunteer did two trials, one with tryptophan supplementation (TRP) and the other with placebo (PLB). Various body fuel, plasma amino acid and renal function parameters were analysed in relation to fatigue data obtained using the Borg test. Blood pressure, pupil size and haematocrit values were also monitored. The parameters obtained were used to examine the principal components of fatigue in said test. ObjectiveTo confirm that, under test conditions, oral L-tryptophan supplementation has a favourable influence on fatigue perception during exercise. ResultsThe principal components of fatigue, as reflected by the Borg test in this study, fit the following model: Perception of fatigue attained=8.406050586+(0.126275247*% load intensity)−(0.031521537*cholesterol mg/dl)+(0.051002322*HDL cholesterol mg/dl)−(0.017130681*tryptophan mmol/ml)−(0.004545865*glycinemmol/ml)+(0.082894085*methioninemmol/ml). (Multiple correlation coefficient=0.90; coefficient of determination R2=0.82; adjusted R2=0.81; standard error: 1.82; observations: 75). Renal functionUrea: (TRP: 45.6±6.5mg/dl vs. PLB: 44.1±5.7; p<0.4); creatinine: (TRP: 90.4±12.0 vs. PLB: 88.4±11.8mg/dl; p<0.9); resting pupil size: (TRP: 0.38±0.07AU vs. PLB: 0.35±0.08AU; p<0.01); haematocrit: (TRP: 45.3%±1.5% vs. PLB: 46.1%±2.6%; p<0.40). ConclusionsHigher tryptophan levels reduced the increased subjective perception of fatigue (SPF). In the component analysis the impact of tryptophan was estimated as 4% in our model. Tryptophan supplementation did not affect renal function. Tryptophan supplementation altered pupil size. At the dose used, tryptophan supplementation proved effective for the first 2h following the last intake of the tryptophan supplement.
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