Men Taking Tyrosine Supplements Able to Exercise in Heat for Longer

An increased level of dopamine in the brain improves the capability of exercising in hot conditions. Tyrosine is the amino acid responsible for dopamine synthesis. This study was conducted to determine whether the use of tyrosine as a food supplement to increase brain dopamine levels would have similar effects. It was based on exercise trials on eight healthy males. The results showed that males who were supplemented with tyrosine had an enhanced capacity of exercising in heat due to increased tolerance to high temperatures.

The exercising capacity of an individual is less at high temperatures compared to that at moderate temperatures. An increase in the body temperature causes changes within the central nervous system, which induces fatigue. However, no studies have been able to identify the exact neurobiological cause behind this. A previous study, which was conducted using bupropion to increase brain dopamine levels, showed that bupropion increases the capacity of exercising at warm temperatures (86 F), but had no effect at low temperatures (64 F). The present study was attempted to examine the efficiency of tyrosine supplementation in enhancing exercise performance at high temperatures of about 86 F.

* Eight healthy males with an average age of 32 years, who were regular exercisers and were not accustomed to exercising in hot weather, participated in the study.
* The test exercise involved cycling in a climate chamber maintained at 86 F with 60 percent relative humidity.
* Initial laboratory tests were performed using blood and urine samples. Two separate exercise trials were then carried out.
* Before the exercise trials, all participants were given a tyrosine-supplemented drink or a placebo drink, at random.
* They were then asked to cycle until exhaustion. Their body core temperatures, rates of exhaustion and perceived exertion were then recorded. Urine and blood samples were also taken for laboratory analysis.

Data/Results/Key findings
* Those who drank tyrosine-supplemented drinks exercised longer at warm temperatures than those who were given placebos.
* There was a threefold increase in the ratio of tyrosine to other amino acids in tyrosine-supplemented subjects.
* There was no difference in blood glucose, hydration status (urine osmolality), heart rate, and body and skin temperatures between the two groups.
* The rate of exhaustion (RPE-rate of perceived exertion) was slower after 45 minutes in tyrosine-supplemented subjects.

Next steps/Shortcomings
In the present study, though the rate of perceived exertion was measured, the central fatigue was not measured directly. The authors of this study suggest that future studies should focus more on frequent measurements of rate of perceived exertion and skin temperatures to better highlight the effects of tyrosine supplementation.

There is conclusive evidence that tyrosine supplementation improves the capability of exercising in hot conditions. Brain dopamine plays a major role in voluntary movement, mood, motivation, and endurance. In this study, due to the increased availability of tyrosine through supplementation, there was a sustained motivation level to exercise, and the tolerance to heat was enhanced. This allowed the participants, who were supplemented with tyrosine, to exercise for a longer time. In hot conditions, a combined stress of heat and exercise leads to more rapid firing of brain neurons and the tyrosine concentration is depleted. Hence, tyrosine supplementation helps in maintaining the dopamine levels and enhancing performance during high intensity workouts.

For More Information:
Oral Tyrosine Supplementation Improves Exercise Capacity in the Heat
Publication Journal: European Journal of Applied Physiology, March 2011
By Les Tumilty; Glen Davison; Aberystwyth University, Wales

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