Effects of high-dose large neutral amino acid supplementation on exercise, motor skill, and mental performance in Australian Rules Football players

Journal Title (Medline/Pubmed accepted abbreviation): Appl Physiol Nutr Metab
Year: 2011
Volume: 36
Number: 5
Page Numbers: 671-681

Summary of background and research design:

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.

Summary of research findings:
  • At baseline, the fatiguing exercise resulted in a moderate increase in the mean repetition time for the RMST (6%) and RAT (5.7%) results, a significant reduction in the test performance index (–16%; P = .03), and a moderate reduction in accuracy (11%). Thus, the exercise protocol was effective in inducing fatigue-related performance decrements.
  • There was a small improvement from baseline in the mean repetition time for the RMST results in the tryptophan-depleting treatment (–3.0% vs. baseline) arm versus a small decrement in the tryptophan-containing treatment arm (+2.4% vs. baseline), but no significant differences between groups (effect sizes were small vs. baseline in either case).
    • In the RAT, the mean repetition time decreased for both treatments, with the tryptophan-depleting treatment causing a 5.2% decrease vs baseline (moderate difference) and the tryptophan-containing treatment causing a 2.9% decrease vs. baseline(small difference)
  • Skill performance (handball mean score during the RMST) was moderately improved from baseline in the tryptophan-depleting (+7.4%) and tryptophan-containing (+8.0%) treatment arms.
    • Test performance index (repetition score/total repetition time) in the RMST decreased from pre- to postexercise by 16% (P < 0.05), 5.1%, and 13% (P = 0.06) for the baseline and the tryptophan-depleting, and tryptophan-containing treatment arms, respectively.
  • Fatigue and vigor scores were not improved in either treatment arm.
  • Overall, cognitive function scores (e.g., Stroop Color-Word score) were improved from baseline for both the tryptophan-depleting and tryptophan-containing treatment arms.
    • However, the individual color and word scores were improved in the tryptophan-depleting treatment arm and decreased in the tryptophan-containing treatment arm.
  • Total mood disturbance scores were increased to a greater degree in both the tryptophan-depleting (+11.4 units) and tryptophan-containing treatment arms (+13 units) versus baseline (+5.9 units) from pre- to postexercise.
  • Plasma glucose and lactate levels were not different between groups.
  • The ratio of free tryptophan to total free LNAA reflected the 2 protein drinks’ composition.

Interpretation of findings/Key practice applications:

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.


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