Failure of Oral Tyrosine Supplementation to Improve Exercise Performance in the Heat.

• Autores: Les Tumilty, Rhys Thatcher, Glen Davison, Manfred Beckmann
• Localización: Medicine & Science in Sports & exercise: Official Journal of the American College of Sports Medicine, ISSN 0195-9131, Vol. 46, Nº. 7, 2014, págs. 1417-1425
• Idioma: inglés
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• Resumen

  • AB Purpose: Acute oral tyrosine administration has been associated with increased constant-load, submaximal exercise capacity in the heat. This study sought to determine whether self-paced exercise performance in the heat is enhanced with the same tyrosine dosage. Methods: After familiarization, seven male endurance-trained volunteers, unacclimated to exercise in the heat, performed two experimental trials in 30[degrees]C (60% relative humidity) in a crossover fashion separated by at least 7 d. Subjects ingested 150 mg[middle dot]kg-1 body mass tyrosine (TYR) or an isocaloric quantity of whey powder (PLA) in 500 mL of sugar-free flavored water in a randomized, double-blind fashion. Sixty minutes after drink ingestion, the subjects cycled for 60 min at 57% +/- 4% peak oxygen uptake (V[spacing dot above]O2peak) and then performed a simulated cycling time trial requiring completion of an individualized target work quantity (393.1 +/- 39.8 kJ). Results: The ratio of plasma tyrosine plus phenylalanine (tyrosine precursor) to amino acids competing for brain uptake (free-tryptophan, leucine, isoleucine, valine, methionine, threonine, and lysine) increased 2.5-fold from rest in TYR and remained elevated throughout exercise (P < 0.001), whereas it declined in PLA from rest to preexercise (P = 0.004). Time-trial power output (P = 0.869) and performance (34.8 +/- 6.5 and 35.2 +/- 8.3 min in TYR and PLA, respectively; P = 0.4167) were similar between trials. Thermal sensation (P > 0.05), RPE (P > 0.05), core temperature (P = 0.860), skin temperature (P = 0.822), and heart rate (P = 0.314) did not differ between trials. Conclusions: These data indicate that acute tyrosine administration did not influence self-paced endurance exercise performance in the heat. Plasma tyrosine availability is apparently not a key determinant of fatigue processes under these conditions.