Amino Acids: Their role in endurance training

Amino Acids and Performance
by Bob Seebohar, MS, RD, CSSD, CSCS


Amino acids are the building blocks for skeletal muscle as well as digestive enzymes, hormones, antibodies and other body proteins necessary for optimal functioning. Of the 20 amino acids in the body, there are two types: essential and non-essential. There are eight essential amino acids including — leucine, isoleucine, lysine, methionine, phenylalanine, theonine, tryptophan, and valine. The term essential is used because the body cannot synthesize these amino acids, making it necessary to obtain them from the diet. The twelve non-essential amino acids are equally important, but most of the time can be synthesized in the body at a rate that equals demand so dietary intake is not as crucial. Complete proteins include all of the essential amino acids, and are considered higher quality proteins. Animal proteins (including dairy, poultry, eggs, beef, and pork) and soy protein (plant protein) are considered complete proteins. Incomplete proteins are missing one or more of the essential amino acids, and are therefore characterized as lower quality proteins. Eating a variety of animal and plant sources of protein is the best way to obtain all essential amino acids in the diet.

Of particular interest to endurance athletes are the amino acids, valine, leucine, isoleucine and glutamine.  The Branched Chain Amino Acids (BCAA’s), valine, leucine and isoleucine, are metabolized differently than other amino acids. During prolonged exercise, BCAA’s are taken up by the skeletal muscle rather than the liver in order to contribute to energy production (oxidative metabolism). Making up one third of the muscle amino acid pool, BCAA’s can become quickly depleted with exhaustive endurance exercise.

Glutamine is the most abundant amino acid in the body accounting for greater than 60% of the total intramuscular free amino acid pool. Many cells in the body use glutamine as a fuel for growth and is synthesized in both skeletal muscle and in adipose tissue in addition to the lungs, liver and brain.

There is evidence that during times of stress the body cannot produce enough glutamine to keep up with demand which in turn can reduce performance, immune function and affect mood state. Athletes at risk for inadequate stores of glutamine include those not eating enough calories, carbohydrates or protein or those participating in strenuous endurance events.  The plasma glutamine response to training is thought to be biphasic that is an increased concentration during acute exercise followed by a decreased concentration after more prolonged exercise.  Several authors have reported plasma glutamine levels decreased as much as 25% after running a marathon. Therefore, the need for proper daily eating is important to help maintain normal glutamine levels.

Central Fatigue Theory and Endurance Athletes
There has been an increased interest in the mechanism behind central fatigue and the influence of BCAA’s on fatigue during and after exercise. The central fatigue theory suggests that prolonged exercise lowers BCAA plasma (blood) concentration through amino acid oxidation and increases the plasma concentration of free fatty acids (FFA). The increased FFAs compete with tryptophan for binding sites on albumin which is a transporter protein. This cascade effect ultimately leads to an increase in free tryptophan levels in the brain where tryptophan is converted into the neurotransmitter serotonin. Serotonin can have a sedative effect on the central nervous system and compromise athletic performance.

During prolonged exhaustive exercise, two mechanisms have been suggested to contribute to an imbalance between BCAA and tryptophan.

1) In the latter stages of prolonged exercise, low blood sugar stimulates gluconeogenesis which is the synthesis of new glucose from non-carbohydrate sources or amino acids. In particular BCAA’s are broken down to be used as a fuel source. When this occurs the BCAA/tryptophan ratio is reduced leaving a relatively high level of tryptophan to enter the blood brain barrier and convert to serotonin.

2) FFA’s also are broken down in higher amounts as glycogen becomes depleted during endurance exercise. Free fatty acids are water soluble and therefore bind to albumin for transport in the blood. Tryptophan also binds with albumin. Because there is a competition between tryptophan and FFA for albumin binding sites, the excess free tryptophan crosses the blood-brain barrier to convert to serotonin.

Immune Response
BCAA’s play a role in the immune response following exercise. Researchers have concluded that the administration of BCAA’s may improve serum glutamine levels leading to a lesser incidence of sickness following exercise. Following an Olympic distance triathlon or 30K run Basset studied the immune response in a group which was administered BCAA’s versus a second group administered a placebo. The results indicate that BCAA supplementation recovers plasma glutamine concentration. The amino acids also positively affect the immune response. (Basset, 2000)

A follow-up study again proved the benefit of supplementing with BCAA’s during exercise in respect to immune function. Twelve elite male triathletes swam 1.5 km, cycled 40 km, and ran 10 km (Olympic triathlon) in the Sao Paulo International Triathlon held in April 1997 and April 1998. In both events, six athletes received BCAA’s and the others received a placebo. The athletes from the BCAA group had the same levels of plasma glutamine, before and after the trial, whereas those from the placebo group showed a reduction of 22.8% in plasma glutamine concentration after the competition. The BCAA group showed a 33.8% reduced incidence of infection due to improvement in immune response following exercise over the placebo group.

Overtraining is described as an imbalance between training and recovery and usually results in a decrease in exercise performance. During a period of overtraining glutamine stores can be depleted faster than the body can replenish them. Overtrained endurance athletes typically suffer from chronic low plasma glutamine levels. Researchers have effectively correlated overtraining syndrome (OTS) to amino acid imbalances. Decreased performance, decreased mood, and increased incidence of infections characterize these amino acid imbalances caused by OTS. Athletes who exercise extensively and are suffering from OTS may become immuno-suppressed leading to infection and increased upper respiratory tract infections (URTI). Supplementing with glutamine in order to maintain normal levels of intramuscular glutamine is critical in maintaining a strong immune system and preventing the breakdown of skeletal muscle.

Conditions of severe stress such as exposure to extreme altitude, massive trauma, and burns have been shown to decrease glutamine concentrations similar to the reductions noted in endurance athletes after training and competition. Supplementation with glutamine has been shown to improve recovery rates in these patients, and has also been linked to improve gut function.
Endurance Performance
Glutamine supplementation is most effective during those times of high-volume and/or high intensity training, particularly if you are in danger of OTS. Though glutamine may not offer a direct ergogenic performance enhancing effect, it will offer insurance for the maintenance of skeletal muscle and immune function. It’s anti-catabolic and immuno-stimulant properties are critical during times of heavy training. There is also evidence supporting the use of glutamine to enhance glucose replenishment. Using glutamine in conjunction with carbohydrates and proteins further improves glycogen re-synthesis. Sustaining adequate glutamine levels may also help modulate the damaging effects of cortisol. Supplementation with 6 – 8 grams/day of BCAA and glutamine has been shown to decrease protein degradation during ultra-distance triathlon competition; decrease exercise induced muscle damage after prolonged running, and improve 40K cycling time trial performance.

Although the direct physiological association and mechanism between glutamine and endurance performance is still a bit unclear in the scientific community, the consistent increases and decreases of plasma glutamine experienced in different athletes participating in different modes of exercise, duration and intensity make it a valuable blood marker monitoring tool for both positive and negative adaptations to training.

Studies have investigated the effect of BCAA supplementation immediately before, during, and after endurance exercise. There is some evidence to support BCAA supplementation during endurance exercise but it has been criticized due to methodological errors and lack of control (Davis et al., 2000). It is difficult to separate the effect of carbohydrate and BCAA’s on the brain and muscle, but data does exist to support a beneficial role of the two combined on central fatigue during endurance exercise. The evidence is stronger to support supplementation of BCAA’s during recovery of endurance exercise and to reduce incidence of infection.

However, new evidence supports that oral ingestion of BCAA’s during exercise can have an anti-catabolic effect on skeletal muscle. Specifically, leucine can stimulate muscle protein synthesis (Lynch, 2003). When combined with carbohydrate feeding during exercise, BCAA’s stimulate protein synthesis and maintain whole body protein balance better than carbohydrates alone (Koopman, 2005). When BCAA’s were consumed during resistance training Shimomura et al. (2006) found a significant reduction in delayed onset muscle soreness (a.k.a. DOMS). Additionally, when swimmers consumed 12 grams of BCAA’s they had reduced post-exercise urinary protein metabolites suggesting that they experienced reduced protein turnover (Tang, 2006).

In another, more recent study (Matsumoto, 2007), the consumption of a 16-ounce beverage containing 2 grams of BCAA’s with 0.5 grams of arginine and 20 grams of carbohydrate at the beginning of a one-hour moderate (50% of maximal work intensity) exercise session, suppressed skeletal muscle protein breakdown.  Previous studies have shown that higher doses of BCAA’s produce a positive effect but this study provided evidence that even a low amount of BCAA’s can be beneficial in preventing muscle protein breakdown which is seen in moderate to intense exercise.

Amino Acid Recommendations

Most naturally occurring food proteins contain only 4 to 8% of their amino acid as glutamine. Though glutamine is available in small quantities from a variety of foods, such as cabbage, beets, beef, chicken, fish, beans and dairy products, it is easily destroyed by cooking. Raw vegetables can be a good source of glutamine though evidence suggests that dietary glutamine is not easily absorbed through the intestine. Another option is obtaining glutamine from dietary supplements, which may be absorbed more efficiently.

1. Supplement with 5 – 10 grams of glutamine during a pre-exercise meal approximately 1-2 hours before a long exhaustive training session (e.g. greater than 3 hours).
2. Supplement with 0.5 – 1.0 gram/hour during training (included in a carbohydrate, electrolyte drink).
3. Supplement with approximately 5 grams of glutamine immediately post-exercise (included in a recovery drink).
No problems of toxicity from glutamine supplementation have been observed. However, it is important to note that glutamine is unstable in solution and should not be kept in that form for more than a few hours at room temperature, and should not be added to hot drinks. In addition, ingesting single amino acids can cause imbalances of others, so ingesting as an ingredient in a sport drink or whole food is preferred.

It is recommended that endurance athletes consume BCAA’s at moderate levels in order to assure no negative affects. However, supplementing at moderate doses can offer a reduced incidence of infection, improved mental energy and assurance of adequate levels of a circulating amino acid pool.

1. The breakdown of protein, particularly BCAA’s occurs as carbohydrate stores decline. This happens primarily in long exhaustive exercise. The first line of defense is to keep a healthy level of blood sugar by supplementing with a carbohydrate drink during intense exercise and lasts longer than 1 hour. Supplement with 45-80 grams of carbohydrate in a 6-8% solution per hour of exercise.

2. The release of serotonin (the fatigue hormone) occurs when BCAA’s decline and tryptophan increases. Supplementing with BCAA’s during exercise may help maintain a healthy ratio. Supplement with a carbohydrate electrolyte drink that contains BCAA’s during exhaustive endurance exercise. Consume 2 – 6 grams of BCAA’s per hour of exercise (no ill effects have been shown with up to 30 grams per day).

3. Consider supplementing BCAA’s following long exhaustive exercise. This will help you remain mentally and physically strong through consecutive days of hard endurance training through improved immune response and reduced incidence of infection. Supplement with 4 – 6 g BCAA’s following your hardest training sessions.

4. Consider BCAA supplementation if you participate in extensive endurance training and ingest an inadequate amount of carbohydrate in your daily eating program.

It has been theorized that supplementing with BCAA’s in doses considerably larger than what is recommended can cause some adverse effects like inhibiting the absorption of other amino acids, slowing water absorption in the gut and can potentially increase the need for thiamin. A rule of thumb is to only consume the recommended amount of amino acids.

For more information, check out our article on free form amino acids.

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7 replies
  1. George
    George says:

    I usually add glutamine to my coffee and drink it within a few minutes. You state that glutamine should not be added to hot drinks, but I assume you mean if they are stored for a period of time and that it is ok if they are consumed immediately. Is this an accurate interpretations, or should I avoid adding glutamie to hot drink no matter how quackly they are consummed.

  2. Robert Kunz MS
    Robert Kunz MS says:

    Glutamine’s stability in both liquids and in heat has greatly improved in the last few years due to ingredient suppliers advances in technology. We use glutamine in our EFS liquid shot and have tested its stability for over a year with practically no degradation. As long as you are getting your glutamine from a reputable supplier and one that can verify its stability then you will be fine. I would contact your glutamine supplier and ask.

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