Going the Distance
by Alan Christianson, N.D.

Supplements to improve athletic endurance — what works and what doesn't?

runnerWhile training is the single most important factor in enhancing sports performance, athletes are always looking for ways to supplement their workouts. The search for an extra edge makes so-called "performance boosters" alluring. There are certainly plenty of substances on the market that promise to improve physical performance, tempting both weekend warriors and competitive athletes. Some of these substances, called ergogenics, really do enhance performance, while others rely almost solely on marketing hype. And some products are appropriate for strength-training athletes but not necessarily for stamina training.

Through a variety of mechanisms, ergogenics improve strength and endurance. They are typically used by endurance athletes who participate in sports that last more than three hours. While marathoners, ultramarathoners, triathletes and stage bicycle racers fall into this category, the recreational athletes who run, hike, mountain bike and cross-country ski may also find these supplements useful in reaching greater heights. The following information will help you choose the supplements that are scientifically proven to increase your endurance and speed your recovery versus the ones that are stuck at the starting line.

An Amino Acid Trip
Some types of amino acids appear to have beneficial effects for endurance athletes, while studies show other types have little or no effect.

Branched chain amino acids (BCAAs), including leucine, isoleucine and valine, are essential to aerobic metabolism. As supplements, they can help fight fatigue and increase energy. During aerobic activity, BCAA levels decrease, causing a greater perception of fatigue and less available fuel. Here's why: When BCAAs decrease, the ratio of BCAAs to tryptophan (also an amino acid) is skewed in favor of tryptophan, which is a precursor to serotonin. And increased serotonin production during exercise enhances the perception of fatigue. However, by maintaining adequate BCAA levels in the bloodstream, serotonin production is kept in check.

In addition to causing the perception of fatigue, BCAA decline also limits available fuel; glycogen metabolism — in other words, the breakdown of stored sugar — becomes less efficient and less fuel is available.1

Edward Blomstrand, Ph.D., of Research Laboratories, Stockholm, Sweden, observed seven trained cyclists given one 3-g dose of BCAAs. The athletes, who had exercised to exhaustion the night before to produce low levels of muscle glycogen, exercised for an hour. During the activity, they were given either BCAAs or placebo. Although physical performance was the same for both groups, the group taking BCAAs perceived less exertion than the placebo group.2

These results are consistent with other studies that have shown BCAAs tend to reduce perceived fatigue but do not affect actual performance in events lasting less than three hours.3

Carnitine is a conditionally essential amino acid, meaning the body can make it in most, but not all, circumstances. Its prime role is shuttling free fatty acids — those available in the bloodstream for use as fuel — into the part of the cell where energy is made. Skeletal and cardiac muscle cells are especially dependent on adequate carnitine for their energy. Carbohydrates, fats and proteins all contribute to energy production, but trained athletes use a higher ratio of stored fat to carbohydrates for energy than the untrained. Because more calories are stored as body fat than as carbohydrates, being able to use more fat means that more energy is available.

Many researchers have speculated that supplemental carnitine may help improve the ability of cells to use fats; however, research reviewed at the Cape Town Medical School, South Africa, showed that chronic carnitine ingestion had no effect on fat metabolism.4

Physiologist Petro Colombani of Zurich, Switzerland, and colleagues studied the effects of carnitine on trained endurance athletes during and after a marathon. In this double-blind study, seven men took 2 g carnitine two hours before the 26.2-mile run and the same dose after 13.1 miles, while seven men took placebo. Supplementing with carnitine increased carnitine in the blood but did not significantly change running time or fatigue level. The morning after the run, a test was given to evaluate athletes at levels lower than their maximum heart rate. Carnitine did not alter the athletes' performance, metabolic efficiency or recovery5 and seems to have no benefit for endurance athletes.

Creatine, or creatine monohydrate, is an amino acid that helps muscles produce energy and increases muscle mass via hydration. Although it has been shown to benefit strength-training athletes,6 studies show it actually decreases endurance. William Cook, Ph.D., of Texas A&M University, College Station, gave 20 g creatine per day to 12 cyclists for five days. Supplementation resulted in a 1.58 percent decline in peak power (maximum pedaling force) in the creatine group.7

Considering the threat to fluid stores and research suggesting impaired performance, creatine is not recommended for endurance athletes. However, strength-training athletes may find it beneficial.

Hormones: Helpful or Harmful?
Like creatine, androgens may help strength-training athletes, but research shows they are unlikely to enhance performance for endurance athletes. And despite the hype about androstenedione a year or so ago, it also has not held its own in the laboratory.

Androgens are hormones that impart male secondary sexual properties including voice deepening, genital maturation, semen production and body hair growth. Androgens used to increase sports performance are primarily testosterones and their precursors. These hormones can help strength athletes by increasing lean body mass, but for endurance athletes extra mass is an impediment. Endurance athletes would be wise to steer clear of androgens in general.

Androstenedione, technically a hormone precursor, is converted in the body to testosterone and estrogens. Some data show androstenedione to increase testosterone within 1.5 hours of taking the supplement, whereas other reports show no increase in testosterone levels but an increase in estrogenic compounds. These variations can be attributed to the subjects' current hormone levels. This is why androstenedione should not be used by young athletes.8

No studies have evaluated andro- stenedione as an endurance aid. Since more powerful androgens do not affect endurance, there is little chance androstenedione will, either. In addition, the International Olympic Committee includes androstenedione on its list of banned substances.

There is no data, researched or hypothetical, supporting androstenedione as an ergogenic supplement.

Ginseng By Any Other Name
Despite herbal lore to the contrary, the ginsengs have yet to stand up to scientific scrutiny as performance enhancers.

Chinese ginseng
Chinese ginseng (Panax ginseng), also called Ren Shen, has certainly captured the hopes of those seeking more energy. The roots of 3- to 7-year-old panax ginseng plants contain the active constituent ginsenoside.9

In animals, panax has been shown to increase swimming endurance and stress resistance.10 In several human studies that have evaluated ginseng as an ergogenic, however, results have been equivocal or negative.11 In a representative study, Calvin Meyer, M.D., a neuroendocrinologist in Detroit, Mich., and colleagues studied physiologic and psychological effects of ginseng on aerobic exertion. They evaluated 36 healthy men who took ginseng for eight weeks. Nine took 200 mg/day, nine took 400 mg/day and 18 took placebo. Studies were done before and after the trial to evaluate aerobic performance. At either dose, ginseng provided no significant change in perceived exertion, oxygen consumption or other markers of exertion.12 Furthermore, ginseng users should practice caution when also taking steroid drugs such as prednisone because ginseng can enhance the effects of the drug.

Siberian ginseng
Siberian ginseng (Eleutherococcus senticosus), also called Ci Wu Jia, is not a true ginseng but is called one because of its use as a general tonic. Clinically, its most authenticated effect is lowering the risk of infection during stressful times.9 As with panax, animal studies have shown an increase in maximal swim times. However, human studies on endurance have shown no benefit. For example, 20 distance runners participated in a study at Old Dominion University, Norfolk, Va., in which 10 were given Siberian ginseng extract and 10 placebo. Initially and during the eight-week study, the runners completed trials of a 10-minute treadmill run at their 10-km race pace and a maximal treadmill test. Researchers measured heart rate, oxygen consumption and perceived exertion. No significant differences were seen in perceived exertion, measured parameters or time to exhaustion.13

Rehydrating: Beyond H20
Water itself is an endurance aid, and sound hydration strategies are essential in long events.

Glycerol is a nonintoxicating alcohol. It is a product of free fatty acids, which are used in the body's cycle of aerobic energy metabolism. Glycerol increases water in muscles, enhancing hydration. Eight athletes supplementing with 1 g glycerol per kilogram body weight were able to increase their total body water by nearly 1 L — about 2.5 percent — which helped them adapt to heat during prolonged exercise.14

Although this phenomenon has been demonstrated in only a small number of studies, the benefits have been consistent, especially in hot weather.15 For example, researchers at the Department of Medicine, Veterans Affairs Medical Center, Albuquerque, N.M., studied the effects of glycerol on the hydration and performance of 11 athletes exercising in the heat. Before riding to exhaustion, they were given 1.2 g glycerol per kilogram body weight or placebo. During the same levels of intensity, those given glycerol showed lower heart rates than those given placebo. Elevated heart rate is a marker of poor hydration. Additionally, the riders given glycerol ran longer before exhaustion.16

During events lasting longer than three hours, glycerol replacement during exercise may also be beneficial. In addition to taking straight glycerol, athletes may choose from several hydration formulas that now contain this ingredient. At effective dosages, straight glycerol is more economical than formulas.

Phosphate and bicarbonate salts
Phosphate and bicarbonate salts are the body's main pH buffers. Fatigue is related to a decline in muscle pH, which also inhibits aerobic and anaerobic energy production. Based on this, scientists have theorized that buffering metabolic acids with phosphate might enhance endurance and help maintain hydration.

In a double-blind study, researchers evaluated the effects of phosphate loading (4-60 g/day) on the performance of six trained triathletes. They took either 4 g/day of sodium phosphate or placebo for three days before performing both maximal cycling tests and a time trial. Phosphate both increased cycling endurance and raised aerobic threshold (maximum level of intensity at metabolic efficiency).17

Hydration is one of the most critical variables that endurance athletes can control. The longer the event and the hotter the day, the more important it is. To improve hydration, athletes can load for one week with 2 ounces glycerol and 1 ounce phosphate daily. During events longer than three hours, athletes should take fluid replacement formulas that contain glycerol. And considering the low cost of sodium phosphate solution, its lack of side effects and proven efficacy, it is a worthwhile ergogenic for endurance.

On A Chemical Level
Exertion affects the body at a chemical level. Some researchers have speculated that replenishing depleted chemicals can circumvent exhaustion.

Choline is used to make acetylcholine, which aids nerve impulses. Prolonged exercise causes a decline in acetylcholine, which may reduce the ability of nerves to transmit impulses to exercising muscles. Marathon runners have been shown to lose 40 percent of choline during the course of a race. This level of decline has shown compromised nerve junction activity.18 Although a potential for benefit exists, actual benefit from choline supplementation is theoretical because there have been no clinical trials.

Athletes ask for more from their bodies than the average person. Consequently, they have to give more. Supporting with ergogenics, as well as the proper nutrients, during intense training is an important part of this. Keep in mind, however, the most effective way to enhance performance will continue to be diligent training. Take care of your body so that it can continue to take care of you.

Alan Christianson, N.D., has a private practice in Scottsdale, Ariz.

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10.Saito H, et al. Effect of Panax ginseng root on exhaustive exercise in mice. Jpn J Pharmacol 1974;24:119-27.

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12.Engels HJ, et al. No ergogenic effects of ginseng (Panax ginseng C.A. Meyer) during graded maximal aerobic exercise. J Am Diet Assoc 1997 Oct;97(10):1110-5.

13.Dowling EA, et al. Effect of Eleutherococcus senticosus on submaximal and maximal exercise performance. Med Sci Sports Exerc 1996 Apr;28(4):482-9.

14.Robergs RA, et al. Glycerol biochemistry, pharmacokinetics: clinical and practical applications. Sports Med 1998 Sep;26(3):145-67.

15.Inder WJ, et al. The effect of glycerol and desmopressin on exercise performance and hydration in triathletes. J Med Sci Sports Exerc 1998 Aug;30(8):1263-9.

16.Montner P, et al. Pre-exercise glycerol hydration improves cycling endurance time. Int J Sports Med, 1996 Jan;17(1):27-33.

17.Kreider RB, et al. Effects of phosphate loading on metabolic and myocardial responses to maximal and endurance exercise. Int J Sport Nutr 1992 Mar;2(1):20-47.

18.Kanter MM, et al. Antioxidants, carnitine, and choline as putative ergogenic aids. Int J Sport Nutr 1995 Jun;5 Suppl:S120-31.