Journal Title (Medline/Pubmed accepted abbreviation): Appl Physiol Nutr Metab
Page Numbers: 671-681
Background:Fatigue that accumulates over time in a team sport affects the amount and intensity of performance as well as skill execution and decision making. The causes of fatigue are multifactorial and include both central and peripheral factors. Central nervous system-based fatigue may be caused by serotonin, as depletion of serotonin delays fatigue onset. Serotonin is produced from tryptophan and requires a transporter for activity; therefore, transporter inhibition by large neutral amino acids (LNAA) such as the branched-chain amino acids (BCAA) may delay fatigue onset.
Hypothesis/Purpose: The purpose of this study was to evaluate the effect of a high-dose LNAA supplement on reactive motor skills, agility, and cognitive performance in Australian Rules Football (ARF) players performing high-intensity intermittent exercise.
Subjects: Fifteen sub-elite ARF players (mean age, 22 ± 3 y; height, 1.79 ± 0.08 m; body mass, 83.1 ± 17.3 kg; maximal oxygen consumption [VO2max], 50.3 ± 8.8 mL/kg/min) participated in the study. Results are based on 13 players who completed the study.
Experimental design: Randomized, double-blind, cross-over
Treatments and protocol:
Players were randomized in a counterbalanced manner 7 days apart to either a tryptophan-containing (2.3 g) protein drink or the protein drink without tryptophan (13.5 g leucine, 8 g isoleucine, 8.9 g valine, 5.7 g phenylalanine, 6.9 g tyrosine) (i.e., tryptophan-depleting) that was consumed immediately before a low-glycemic-index, high-carbohydrate meal. An exercise session was started 3 hours after the meal and consisted of a warm-up (600 mL sports drink and exercises), reactive motor skills testing (RMST; 12 reps with 60-sec recovery), reactive agility testing (RAT), and 30 minutes of fatiguing exercise (modified yo-yo intermittent endurance test), followed by RMST and RAT retesting. A baseline exercise session without any supplementation was performed before randomization. Mood states and cognitive function were assessed before warm-up and after the exercise session. Blood samples for glucose, lactate, and free amino acids were collected immediately before supplementation and the exercise session and after the fatiguing exercise.
The consumption of serotonin-depleting LNAAs improved certain aspects of reactive agility, skill performance, and cognitive function when players were fatigued. However, mood states were adverseline affected. In addition, the high-dose supplementation resulted in a highly powdery suspension of low palatability. The high doses of amino acids used in this study may be prohibitively expensive for many athletes. Lower doses have not yet been evaluated; therefore, further research is necessary.