Purpose:An acute dose of tyrosine, 1 hour before exercise has been associated with improved exercise capacity in a warm condition although the same dose has failed to demonstrate any benefit on exercise performance at the same environmental temperature. The present study sought to determine whether administering different doses of tyrosine across trials would demonstrate whether an optimal dose of tyrosine exists for improving exercise performance in the heat. Method:Following familiarisation, 8 healthy male volunteers who were unacclimated to exercise in the heat, performed 4 experimental trials at 30ºC/60% relative humidity, consuming one of four drinks (placebo, 150 mg kg body mass -1, 300 mg kg body mass-1or 400 mg kg bodymass -1) in a randomised crossover design, separated by at least 7 days. In the hour prior to exercise, participants consumed one of the four experimental drinks before exercising for 1 hour at 10% ∆ (129 ± 17 W) and then completing a simulated time trial as quickly as possible which requir ed the completion of an individualised target work quantity (326 ± 37 kJ). Results:Time trial time (P= 0.553) and time trial power output (P= 0.281) remained similar across all trials. The plasma ratio of tyrosine: ∑LNAA was similar at rest between all trials (P = 0.657) but increased significantly from rest in all tyrosine conditions (P < 0.01;). The tyrosine ratio increased 4.8 fold from baseline in LOW, 7.3 fold in MED and 7.3 fold in HIGH. Core temperature (P= 0.326), skin temperature (P= 0.127), heart rate (P> 0.05), Ratings of perceived exertion (P> 0.05) and thermal sensation (P> 0.05) also remained similar across all trials. Conclusion: The data demonstrates that acute administration of a range of tyrosine doses has no beneficial effect on exercise performance in the heat despite marked increases in plasma tyrosine concentration.
- Tyrosine, Exercise performance
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Thesis, 2.13 MB, PDF
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