While a few readers had questions about specific routines or training protocols, most questions were (and usually are) focused on dietary supplements. When folks ask me about dietary supplements, the same questions typically come up:
Should I load with
Do I need to take protein after I workout?
What protein should I take?
Is it OK to eat meal replacements during a workout?
Are prohormones safe?
Should I take a fat burner?
And the list goes on. Rarely does a supplement come up that isn't one of the above. However, just yesterday I got a question from a reader about the effects of tyrosine on performance. Coincidentally, this month's International Journal of Sports Nutrition and Exercise Metabolism has a research piece on that very amino acid.
Tyrosine is an amino acid (AA). Remember that protein is made up of many different AA's and the combination of the different AA's determines the actual protein.
Oral doses of tyrosine result in increases in circulating concentrations of something called catecholamine, which are hormones, because tyrosine is a precursor to these hormones.
More specifically, these are epinephrine, norepinephrine, and dopamine and are heavily involved in the regulation of body function during physical stress and exercise. These are all part of the sympathetic nervous system.
Fight Or Flight
Epinephrine and norepinephrine in particular are known as the "fight or flight" hormones because in a situation of stress, they are elevated and prepare the body to fight or flight.
For example, if someone breaks into your house, whether you know it or not, these hormones are kicked into high gear as your mind attempts to make a decision. These hormones are also partly responsible for the increases in metabolism with the ingestion of caffeine, but that's for another article.
It has been hypothesized that under stressful situations, the abovementioned hormones would be quickly depleted because of limited amounts of the precursor tyrosine.
Tyrosine supplements are used by strength athletes because of their supposed effect of activating metabolic pathways. However, few controlled studies have shown an effect of tyrosine supplementation on exercise performance.
However, oral supplementation of tyrosine by humans has been shown to improve stress-induced cognitive and behavioral deficits, in particular working memory, and stress-sensitive focus tasks.
Now the carryover to exercise would be because extended exercise is associated with central metabolic and neuroendocrine changes that may ultimately result in fatigue. If tyrosine could alter this normal fatigue, we may be onto something.
Most of the supplements you see that contain tyrosine contain very low doses (mg), but it may be that regular supplementation with much higher doses (g) are necessary for the desired effect.
However, regular supplementation with such high doses may have adverse health effects in the long term because of the way it affects the sympathetic nervous system, as described above.
The purpose of this particular study was to examine the effects of a single dose of tyrosine ingestion on physical performance and catecholamine levels.
The Researchers Wanted To Learn If This Dose Of Tyrosine:
- extended aerobic endurance
- improve muscle strength and endurance
- increase anaerobic power (e.g., lifting weights)
- alters levels of catecholamines
Healthy, moderately to high physically active males (n=20) participated in this study and refrained from taking any other prescription or over the counter supplements during the course of the study.
This was a randomized, counterbalanced, double-blind, placebo-controlled, repeated measures design.
(* Note: see my previous pieces for explanations of each of these terms.)
The VO2max Tests
All subjects underwent a maximal exercise treadmill test (which is far from a stroll through the park, for those who have never done one). This is used to determine something called VO2max.
| What Is A Maximal Treadmill Test?
A maximal treadmill test is when researchers put you on a treadmill and continue to increase the speed and grade of the treadmill (using a predetermined protocol) until you can no longer run and are essentially about to fall off the back.
In this study, after determining VO2max, subjects then underwent a number of selected physical performance tasks. Subjects underwent 2 exercise load tests: a tyrosine load exercise test and a placebo load exercise test.
The load test in this study required subjects to wear a backpack weighted to 30% of his body weight and using 50% of the VO2max calculated above and a 3% treadmill grade. The grade was then increased to 5% and the speed was adjusted to achieve 70% of each subject's VO2max. This speed and grade was maintained for 120 minutes or until exhaustion, where the participant could no longer continue.
Subjects also underwent a number of physical performance measures to determine
grip strength and endurance, lower body
strength and coordination, and upper body strength and
endurance. Subjects were given either tyrosine (150 mg/kg bodyweight) or placebo.
Plasma tyrosine was elevated, so we at least know the supplement was effectively being taken up by the body. However, tyrosine ingestion had no effect on the catecholamines, epinephrine or norepinephrine.
Similarly, no significant differences were noted for any physical task. Ingestion of tyrosine also did not significantly lengthen time on the treadmill. Basically, the tyrosine supplementation did nothing to enhance (or hurt) the performance.
Some may argue that longer periods of supplementation are necessary to see any resultant effects or potentially that the timing of supplementation was not ideal for an resultant effects.
This was an acute study to determine if tyrosine would enhance performance on a number of levels. The researchers concluded at the end of the piece,
The best recommendation at this time is to continue to get tyrosine from the high protein foods you're eating. Some research suggests the timing of nutrients enhances mental acuity and alertness, so consider eating your protein foods first during your meal."
- Erin E. Sutton, Regina Coll, Patricia A. Deuster. Ingestion of Tyrosine: Effects on Endurance, Muscle Strength, and Anaerobic Performance. International Journal of Sports Nutrition and Exercise Metabolism, 2005, 15, 173-185.