Tyrosine Ingestion and Its Effects on Cognitive and Physical Performance in the Heat.
OBJECTIVE
Ingestion of tyrosine (TYR), a catecholamine precursor, has previously improved aspects of cognitive function and mood during acute stress, although there is limited research exploring the optimal dose relative to blood values. The serum responses of two doses of TYR were investigated (study 1), with the identified "optimal" dose assessed relative to cognitive and physical performance during a military-based protocol in the heat (study 2).


METHODS
For study 1, 21 participants were assigned to one of the following three groups: HIGH (two doses of 150 mg · kg(-1) body mass TYR), LOW (two doses of 75 mg · kg(-1) body mass TYR), and CON (sugar-free drink). Participants ingested TYR in two separate doses (0900 and 1300 h) and remained in the laboratory from 0800 to 1700 h, having blood drawn every hour. For study 2, eight participants completed a military-based load carriage protocol composed of a 60-min walk (6.5 km · h(-1)) followed by a 2.4-km time trial carrying a 25-kg backpack (40°C; relative humidity, 30%) on two occasions (TYR/placebo) in a double-blind counterbalanced crossover design. Cognitive function was assessed before, during, and after exercise.


RESULTS
Study 1 demonstrated that ingestion of a single dose of 150 mg · kg(-1) body mass TYR was equally efficient at elevating serum TYR concentration relative to a double dose. In study 2, exercise heat stress impaired some aspects of cognitive function; however, TYR did not alleviate these decrements (P > 0.05). Furthermore, no difference was observed in any physiological variable between conditions (P > 0.05) or time trial completion time (P = 0.74) between TYR (19.78 ± 3.44 min) and placebo (20.29 ± 3.55 min).


CONCLUSIONS
Despite marked elevations in serum TYR concentration, ingestion of TYR did not influence cognitive function or physical performance during exercise heat stress.
1Applied Sport and Exercise Physiology Research Group, Institute of Sport and Physical Activity Research, Department of Sport and Exercise Sciences, University of Bedfordshire, Bedford, UNITED KINGDOM; 2Sport Science Program, College of Arts and Sciences, Qatar University, Doha, QATAR; and 3Department of Human Physiology, Vrije Universiteit Brussel, Brussels, BELGIUM.
Nicole
N
Coull
Bryna
B
Chrismas
Phillip
P
Watson
Rachel
R
Horsfall
Lee
L
Taylor
D000328:Adult; D001628:Beverages; D001831:Body Temperature; D003071:Cognition / Q000187:drug effects / Q000502:physiology*; D018592:Cross-Over Studies; D019587:Dietary Supplements; D004311:Double-Blind Method; D017079:Exercise Tolerance / Q000187:drug effects / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D008297:Male; D058573:Performance-Enhancing Substances / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics; D011930:Reaction Time; D013647:Task Performance and Analysis; D014443:Tyrosine / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics; D055815:Young Adult
D058573:Performance-Enhancing Substances; D014443:Tyrosine