|This review will show that there is evidence to support the performance enhancement of a few supplements,|
Carbohydrate and carbohydrate metabolites
Carbohydrate is the primary dietary energy source for high-intensity aerobic endurance exercise (> 65-70% VO2max), but endogenous supplies such as muscle and liver glycogen are limited and may become suboptimal within 90 minutes.
Carbohydrate loading procedures may elevate endogenous glycogen stores, postponing fatigue and improving performance in which a set distance is covered as quickly as possible (such as a marathon) by 2-3 percent (Hawley et al., 1997). Additionally, numerous studies support the efficacy of carbohydrate supplementation prior to and/or during such prolonged aerobic exercise tasks to improve performance (Williams, 1998B).
Metabolic by-products of carbohydrate are theorized to provide a more efficient fuel than other carbohydrate sources. Several well-controlled studies by researchers at the University of Pittsburgh have shown that pyruvate, administered as dihydroxyacetone and pyruvate (DHAP), may increase muscle glycogen levels or blood glucose uptake by exercising muscles and enhance exercise performance in untrained subjects.
However, these findings have not been duplicated by other scientists and the ergogenic effect of pyruvate for trained athletes is questionable (Anderson, 1997; Williams, 1998B). Other metabolites, such as fructose 1,6-diphosphate and lactate salts (polylactate) do not provide any ergogenic effect beyond that provided by more natural carbohydrate sources, such as glucose (Swensen, et al., 1994; Williams, 1998B).
Lipids and lipid metabolites
Lipids represent an energy source for mild-to-moderate intensity aerobic endurance exercise (less than 50-65% VO2max), but unlike carbohydrate, endogenous stores of lipids as adipose and muscle tissue triglycerides are abundant. Triglycerides provide free fatty acids (FFA), the primary lipid energy source during exercise. Lipid dietary strategies or supplements attempt to increase FFA oxidation and reduce reliance on endogenous carbohydrate stores, sparing muscle glycogen use and delaying fatigue during prolonged exercise.
Other supplements, such as L-carnitine and caffeine supplementation (discussed below) are theorized to exert similar effects.
Fat loading is a dietary strategy involving increased consumption of dietary fats, up to 70 percent of daily energy intake, in attempts to increase the contribution of endogenous fats as an energy source during exercise. Several preliminary studies have shown some beneficial effects of fat loading, but either the experimental design was not appropriate or the exercise tasks used do not appear to have any application to contemporary sports events (Williams, 1998B).
In a major review, Sherman and Leenders (1995) noted that although the fat loading hypothesis is intriguing, the current scientific literature is not supportive. Medium-chain triglycerides (MCT), oral water soluble supplements that may enter the circulation more readily than normal dietary fats, have been theorized to be a more efficient lipid energy source during exercise. However, recent research by scientists from the Netherlands has not shown any significant contribution of oral MCT to energy metabolism during exercise, and two recent studies have shown that MCT supplementation could actually impair 40-kilometer cycling performance (Williams, 1998B). Nevertheless, in a recent review, Berning (1996) noted that some preliminary research findings were promising, particularly when MCT were ingested with carbohydrate supplements during exercise. Confirming research is needed.
Proteins, amino acids, and related metabolites
Protein supplements have been recommended to athletes to enhance nitrogen retention and increase lean body (muscle) mass, to prevent protein catabolism during prolonged exercise, and to support an increased synthesis of hemoglobin, myoglobin, oxidative enzymes, and mitochondria during aerobic training. Current research suggests that athletes may need slightly more protein than the Recommended Dietary Allowance (RDA). Values suggested for strength-type athletes approximate 1.6-1.8 grams per kilogram body weight, while recommended amounts for endurance athletes approximate 1.2-1.6 grams per kilogram body weight (Lemon, 1996; 1995). Such values may be obtained easily in a typical western diet with adequate animal and plant protein. In general, research with protein supplements in excess of these dietary quantities has shown no beneficial effects on strength, power, hypertrophy of muscle, or physiological work capacity (Williams, 1998B). Amino acid supplements have also been marketed to increase muscle mass and enhance aerobic endurance capacity via various mechanisms.
Arginine and ornithine have been used in attempts to increase human growth hormone (HGH) and/or insulin production, the theory being to increase muscle mass and strength via enhanced hormonal activity.
Limited data are available, but a number of well-controlled studies, including several with experienced weightlifters, reported that amino acid supplementation elicited no significant increases in serum HGH, insulin levels, or various measures of muscular strength or power (Fogelholm, 1993; Kreider et al., 1993; Williams, 1998B).
Potassium and magnesium aspartates are salts of aspartic acid, an amino acid. They have been used as ergogenics, possibly by mitigating the accumulation of ammonia during exercise. The effect of aspartate supplementation on physical performance is equivocal, but about 50 percent of the available studies have indicated enhanced performance (Williams, 1998A). Additional research is needed to study their potential ergogenicity and underlying mechanisms.
Tryptophan (TRYP) and branched chain amino acids (BCAA) are thought to affect the formation of serotonin, a neurotransmitter believed to be involved in the etiology of central nervous system (CNS) fatigue during exercise. However, according to proponents of either TRYP or BCAA supplementation, the hypotheses underlying the serotonin effect on the development of fatigue are diametrically opposite.
In one hypothesis, TRYP serves as a precursor for serotonin, a brain neurotransmitter theorized to suppress pain. Free tryptophan (fTRYP) enters the brain cells to form serotonin. Thus, TRYP supplementation has been used to increase fTRYP and serotonin production in attempts to increase tolerance to pain during intense exercise, thus delaying fatigue. Limited data involving TRYP supplementation are available, but one study reported significant improvements in time to exhaustion at 80 percent VO2max, accompanied by significant reductions in the psychological rating of perceived exertion (RPE). However, research with a more appropriate experimental design did not replicate these findings when subjects ran to exhaustion at 100 percent VO2max. Moreover, other investigators reported no effect of TRYP supplementation on aerobic endurance performance at 70-75 percent VO2max (Williams, 1998B). In a recent review, Wagenmakers (1997) concluded that TRYP supplementation had no effect on endurance performance.
Relative to the second hypothesis, some investigators believe that increased levels of serotonin may induce fatigue by depressing central nervous system functions (Newsholme et al., 1992).
During prolonged aerobic endurance exercise, muscle glycogen may become depleted and the muscle may increase its reliance on branched chain amino acids (BCAA) for fuel, decreasing the plasma BCAA:fTRYP ratio. Because BCAA compete with fTRYP for entry into the brain, a low BCAA:fTRYP ratio would facilitate the entry of fTRYP to the brain, increasing serotonin formation and inducing fatigue. Hypothetically, BCAA supplementation may delay fatigue in prolonged aerobic endurance events by maintaining a high BCAA:fTRYP ratio to mitigate the formation of serotonin. Although several studies support this hypothesis both Wagenmakers (1997) and Davis (1996), in recent reviews, concluded not enough evidence indicates BCAA supplementation is ergogenic.
Davis also noted that carbohydrate supplementation during exercise, by delaying the reliance on BCAA as a fuel, would serve the same purpose as BCAA supplementation.
Research indicates that a vitamin deficiency may adversely affect physical performance, but the overall review of the literature supports the viewpoint that vitamin supplements are unnecessary for physically-active individuals who are on a well-balanced diet with adequate calories. Most studies report that athletes who consume high calorie diets containing the RDA of all nutrients have few vitamin or mineral deficiencies (Armstrong and Maresh, 1996). Several excellent studies have shown that multivitamin/mineral supplementation over prolonged periods, up to eight months, have no significant effects on both laboratory and sport-specific tests of physical performance (Singh et al., 1992; Telford et al., 1992).
Nevertheless, vitamin/mineral supplementation may be recommended for athletes consuming a low-calorie diet for weight control sports (Williams, 1998B).
Some studies have shown that specific vitamins supplements may benefit sports performance in events where excess anxiety may be disruptive. For example, thiamin (B1), pyridoxine (B6), and cobalamin (B12) supplementation has been shown to enhance performance in pistol shooting, possibly because of beneficial effects on brain neurotransmitter functions (Bonke, 1986). Additional research is merited.
Supplementation with several antioxidant vitamins (beta-carotene; vitamin C; vitamin E) has been theorized to prevent muscle tissue damage associated with generation of oxygen free radicals during high-intensity exercise. However, recent reviews suggest that research regarding the value of antioxidant therapy for athletes is ambivalent. Some reviewers (Goldfarb, 1993; Kanter, 1995) note that further investigations are needed to determine the viability of antioxidant supplements in preventing exercise-induced lipid peroxidation and muscle damage. Conversely, other reviewers (Dekkers et al., 1996; Packer, 1997) indicate substantial research suggests that dietary supplementation with antioxidant vitamins has favorable effects on lipid peroxidation and exercise-induced muscle damage.
All reviewers indicate more research is needed to address this issue and to provide guidelines for recommendations to athletes.
Antioxidant vitamins, particularly vitamins C and E, have also been theorized to enhance sport performance.
Although vitamin C supplementation has been shown to improve physical performance in vitamin C-deficient subjects, research supports the general conclusion that vitamin C supplementation does not enhance physical performance in well-nourished individuals (Gerster, 1989). Vitamin E supplementation may increase tissue or serum vitamin E concentration, but a recent review indicates that there is no discernable effect on training or performance in either recreational or elite athletes (Tiidus and Houston, 1995). Nevertheless, Packer (1997) indicates that if antioxidant supplementation ameliorates exercise-induced muscle tissue damage, such supplementation may be beneficial in the long term.
Additionally, some studies have shown that vitamin E supplementation may enhance exercise performance at altitude, but confirming research is needed (Williams, 1998B).
As with vitamins, research indicates that a mineral deficiency may adversely affect physical performance. Iron deficiency is the most common mineral deficiency among athletes, particularly female athletes in weight-control sports, and curing an athlete's iron-deficiency anemia with iron supplementation will return performance to normal.
However, in general, research also indicates that mineral supplements, including multivitamin/mineral compounds, are unnecessary for physically-active individuals who are on a well-balanced diet with adequate calories.
Several minerals have been marketed as potent anabolic agents. Chromium is an insulin cofactor, and its theorized ergogenic effect is based on the role of insulin to facilitate BCAA transport into the muscle. Chromium has been advertised for strength-type athletes. The available research with chromium is limited, and the data available have not been subjected to a critical scientific review. Some early research data do suggest an increase in lean body mass and decreased body fat with chromium picolinate supplementation (Evans, 1989). However, this report was based on flawed studies.
More contemporary research with better experimental protocols replicated these studies and have shown that chromium picolinate supplementation does not increase lean muscle mass or decrease body fat (Clancy et al., 1994; Hallmark et al., 1996; Trent and Thieding-Cancel, 1995). Other research also indicated different forms of chromium, such as chromium chloride, had no effect on body composition (Lukaski et al., 1996).
Boron and vanadium have also been advertised for their anabolic potential. However, the limited data available do not support an anabolic effect of either boron (Ferrando and Green, 1993) or vanadium (Fawcett et al., 1996).
Phosphorus is an essential nutrient present in the diet as a phosphate salt, or phosphate. Phosphate is a component of several high energy compounds, is essential for the functioning of several B vitamins, and is part of 2,3-DPG, essential for oxygen release from hemoglobin. An increased 2,3-DPG level is the prevalent theory underlying phosphate supplementation to endurance athletes. Current research is equivocal as to whether or not phosphate loading may improve physiological functions important to endurance performance.
However, no study has reported decreases in performance, and several recent studies from independent laboratories have shown remarkable similarities relative to increased levels of VO2max (about 10%) following phosphate supplementation. Increases in physical performance have also been documented in four of these studies (Cade et al., 1984; Kreider et al., 1990; Kreider et al., 1992; Stewart et al., 1990). However, a number of confounding variables in previous research have been identified and more controlled research has been recommended (Tremblay et al., 1994).
Although doping (the use of pharmacological ergogenics to improve sports performance) is prohibited, the International Olympic Committee does permit limited use of several nutritionally-related drugs, such as caffeine, alcohol, and alkaline salts.
Caffeine, found naturally in certain foods or beverages, such as cocoa, coffee, and cola drinks, consumed by athletes, has been studied extensively for its ergogenic potential. Caffeine is a stimulant that may improve various metabolic and psychological functions during exercise, and several recent reviews indicate that legal doses of caffeine may enhance performance in a variety of exercise tasks (Graham and Spriet, 1996; Spriet, 1995).
Many studies that have evaluated the ergogenic effect of caffeine on prolonged aerobic endurance tasks greater than one hour have shown beneficial effects. For example, a series of studies from Guelph University in Canada has suggested caffeine may enhance prolonged aerobic endurance performance through increased levels of epinephrine and sparing of muscle glycogen (Graham and Spriet, 1991; Spriet, et al., 1992). Other recent research suggests caffeine may exert an ergogenic effect in shorter endurance events through neurological mechanisms.
For example, caffeine supplementation has been shown to improve performance in a 1,500-meter run, an event which is not dependent on muscle glycogen sparing (Wiles et al., 1992), and caffeine supplementation also has increased work output on a cycle ergometer at a set RPE (Cole, et al., 1996). Because caffeine appears to be an effective ergogenic in legal doses, some investigators have suggested the IOC should reconsider the legal limits determinant for a positive drug test (Spriet, 1995)
Alkaline salts, such as sodium bicarbonate and sodium citrate, are described as antacids in the United States Pharmacopeia (USP) and have been studied as nutritional ergogenics. Taken orally prior to high-intensity anaerobic exercise, alkaline salts may increase the alkaline reserve and help buffer lactic acid in the muscle cell, an effect that theoretically could improve performance in exercise tasks dependent primarily on anaerobic glycolysis. Research indicates that alkaline salt supplementation will increase the serum pH and may enhance performance in exercise tasks, particularly repetitive exercise tasks, that maximize energy production for 1-6 minutes.
Numerous laboratory and field studies support a positive ergogenic effect of sodium bicarbonate supplementation, and several comprehensive reviews (Linderman and Fahey, 1991; Williams, 1992), including a meta-analysis reporting an effect size greater than 0.40 favoring sodium bicarbonate when compared to placebo conditions (Matson and Tran, 1993), conclude that sodium bicarbonate is an effective ergogenic. Studies conducted subsequent to these reviews have provided mixed results but, in general, about half of these more recent studies have revealed ergogenic effects of sodium bicarbonate or sodium citrate on exercise performance. Some beneficial effects have even been noted on prolonged aerobic endurance tasks, a finding that merits additional research (Williams, 1998B)
Numerous dietary supplements are marketed to physically-active individuals. Advertisements insinuate that such supplements may improve energy production, increase muscle mass, decrease body fat, or induce some other possible ergogenic outcome. By and large, many commercial products have not been studied scientifically to validate such advertising claims. However, some data are available for several specific ingredients marketed individually or as part of a multiple-ingredient product.
Choline - Choline, an amine, is found naturally in a variety of foods. A sports drink powder containing carbohydrates, electrolytes, and choline has been marketed recently.
Choline is involved in the formation of acetylcholine, a neurotransmitter whose reduction in the nervous system may be theorized to be a contributing factor to the development of fatigue. Because plasma choline levels have been reported to be significantly reduced following events such as marathon running, choline supplementation has been theorized to prevent fatigue in aerobic endurance tasks.
Research has shown that choline supplementation will increase blood choline levels at rest and during prolonged exercise, and some preliminary field and laboratory research has suggested increased plasma choline levels are associated with a significantly decreased time to run 20 miles.
However, other well-controlled laboratory research has revealed that choline supplementation, although increasing plasma choline levels, exerted no effect on either brief, high-intensity anaerobic cycling tests or more prolonged aerobic exercise tasks (Williams, 1998B). These findings are equivocal and reviewers have recommended more research with choline supplementation, particularly research involving prolonged aerobic endurance exercise tasks (Kanter and Williams, 1995).
Coenzyme Q10 (Ubiquinone) - Coenzyme Q10 (CoQ10), also known as ubiquinone, is a lipid with characteristics common to a vitamin. CoQ10 is found in the mitochondria in all tissues, particularly the heart and skeletal muscles. CoQ10 is also an antioxidant. CoQ10 supplementation has been used therapeutically for the treatment of cardiovascular disease because it may improve oxygen uptake in the mitochondria of the heart. Theoretically, improved oxygen usage in the heart and skeletal muscles could improve aerobic endurance performance.
Although research data suggests CoQ10 supplementation may benefit cardiac patients, several studies have shown that CoQ10 supplementation to healthy young or older physically-active subjects did not influence lipid peroxidation, heart rate, VO2max, or cycling endurance performance (Braun, et al., 1991; Laaksonen, et al., 1995; Snider, et al., 1992; Weston, et al., 1997). One study reported that CoQ10 supplementation was associated with muscle tissue damage and actually impaired cycling performance compared to the placebo treatment (Malm, et al., 1996).
Creatine - Creatine is a nitrogen-containing substance, found naturally in small amounts in animal foods. Acute oral creatine supplementation, daily as creatine monohydrate for approximately 5-7 days, has been reported to increase muscle concentrations of total creatine, both as free creatine and creatine phosphate, a high-energy phosphagen. Several reviews indicate creatine supplementation may be an effective sport ergogenic (Balsom, et al., 1994; Greenhaff, 1995). Subsequent to these reviews, numerous studies have reported a positive ergogenic effect of creatine supplementation, particularly in repetitive, short-duration, high-intensity, short-recovery isokinetic and isometric resistance tests or cycle ergometer protocols. However, in such tests, although some body parts are exercising, the total body mass is stationary.
Thus, the ergogenic effect of acute creatine supplementation may be limited to laboratory tasks in which the body mass does not need to be moved. Acute creatine supplementation also appears to increase body mass (Williams and Branch, 1998). In exercise tasks in which the body mass is moved, research generally has not supported an ergogenic effect of creatine supplementation on sprint swim performance (Burke, et al., 1996) or sprint run performance (Redondo, et al., 1996), and actually may be ergolytic (impair performance) in endurance running because of the acute increase in body mass (Balsom et al., 1993), which may simply be water associated with the oncotic effect of creatine in the muscle. Creatine supplementation has been shown to improve rowing performance (Rossiter et al., 1996), an exercise task in which the body mass is supported, and may theoretically enhance performance in cycling tasks for similar reasons.
Although acute creatine supplementation may enhance exercise performance under certain laboratory conditions, more research is needed to evaluate its efficacy to enhance actual sports performance. Additionally, well-controlled research is needed to evaluate the effect of chronic creatine supplementation on the training response and subsequent competitive sport performance.
Ginseng - Extracts derived from the plant family Araliaceae contain numerous chemicals that may influence human physiology, the most important being the glycosides, or ginsenosides. Collectively, these extracts are referred to as ginseng. Numerous commercial forms of ginseng products are available, including Chinese or Korean (Panax ginseng), American (Panax quinquefolium), and Russian/Siberian (Eleutherococcus senticosus), but the ginseng content may vary considerably (Cui et al., 1994).
Ginseng supplementation has been theorized to mitigate the stress of exercise and possess ergogenic qualities, but the underlying mechanisms have not been determined. Although some earlier studies reported ergogenic effects of ginseng supplementation on exercise performance, a recent comprehensive review by Bahrke and Morgan (1994) indicated that ginseng research with humans has been characterized by numerous methodological and statistical shortcomings. They concluded, in 1994, that there is an absence of compelling research evidence demonstrating the ability of ginseng to consistently enhance physical performance in humans, and that there remains a need for well-designed research.
Several well-controlled studies subsequent to the review by Bahrke and Morgan reported no significant effect of either Panax ginseng, Eleutherococcus senticosus Maxim L (regarded to be Siberian Ginseng), or a standardized ginseng extract on cardiovascular, metabolic, or psychologic responses to either submaximal or maximal exercise performance, or on maximal performance capacity (Dowling, et al., 1996; Engels and Wirth, 1997; Morris, et al., 1996).
Glycerol - Water ingestion is essential to help optimize body water balance and body temperature regulation during exercise under warm environmental conditions. Rehydration during exercise in the heat has been shown to decrease physiological stress as evidenced by a decreased heart rate response, lesser rise in the core temperature, and increased endurance performance.
Hyperhydration before exercise may also be helpful, but has not been shown to be as effective as rehydration (Williams, 1998B). Glycerol (glycerin), an alcohol byproduct of fat hydrolysis, has been studied as a means to enhance the hyperhydration effect. Small amounts of glycerol are mixed with water in set proportions and the water is consumed following normal hyperhydration procedures. Glycerol capsules and a glycerol-containing sports drink are marketed to athletes.
Glycerol-induced hyperhydration, when compared to water hyperhydration alone, has been shown to increase total body water in some (Freund, et al., 1995; Koenigsberg, et al., 1995), but not all (Latzka, et al., 1997) studies. Several studies have shown that glycerol-induced hyperhydration improves cardiovascular responses, temperature regulation, and cycling exercise performance under warm/hot environmental conditions (Lyons, et al., 1990; Montner, et al., 1996).
However, other research has shown that both glycerol and carbohydrate supplementation improved cycling endurance compared to a placebo solution, suggesting carbohydrate supplementation was as effective as glycerol supplementation as a means to enhance performance (Lamb, et al., 1997). Additional research is needed to resolve these equivocal findings, particularly so in sports such as distance running in which the extra body mass (water weight) must be moved as efficiently as possible.
Inosine - Inosine is a nucleoside with a variety of proposed ergogenic effects, including enhancement of aerobic endurance performance by facilitating the delivery of oxygen to the muscles during exercise. Although scientific research is limited, two well-controlled studies did use the recommended supplementation protocol for endurance athletes and reported no beneficial effects of inosine on cardiovascular-respiratory or metabolic functions during submaximal or maximal exercise, nor was there any effect on time to complete a simulated three mile race on a treadmill. Both studies actually suggested inosine could be ergolytic for certain athletic endeavors involving anaerobic glycolysis (Starling, R., et al., 1996; Williams, M., et al., 1990).
L-carnitine - L-carnitine is a vitamin-like compound found naturally in animal foods, particularly meats, and may also be formed in the liver from various amino acids. L-carnitine facilitates the transport of fatty acids into the mitochondria for oxidation and also facilitates the oxidation of several amino acids and pyruvate, functions that theoretically could lead to a sparing of muscle glycogen during exercise and a decreased production of lactate.
However, recent reviews of the available research do not support an ergogenic effect of L-carnitine supplementation on fuel utilization during exercise, maximal heart rate, anaerobic threshold, maximal oxygen uptake, time to exhaustion in various anaerobic or aerobic exercise tasks, or performance in either a marathon or 20-kilometer run (Heinonen, 1996; Wagenmakers, 1991; Williams, 1998B).
Adequate dietary intake of carbohydrate, essential fatty acids, protein, vitamins, minerals and water is necessary to insure optimal physical performance, because a deficiency of any essential nutrient associated with energy production may impair physiological or psychological functions during exercise.
As may be discerned from this review, supplementation with various essential nutrients or commercial dietary supplements will not, in general, enhance exercise performance in well-nourished, physically-active individuals. However, research tends to support an ergogenic effect for some nutritional ergogenics (including alkaline salts, caffeine, carbohydrate loading, and creatine) under certain conditions or for some athletes. Additional research is needed to evaluate the possible ergogenic effects of aspartate salts, choline, glycerol, MCT, phosphates, pyruvate, and certain vitamins (antioxidants; B1, B6, B12; E) for specific conditions mentioned above.
Caution is advised when using any nutritional ergogenic in an attempt to enhance sport performance. As noted above, some products may impair performance. Also, improper amounts may cause various health problems. For example, supplements such as alkaline salts may cause gastrointestinal distress and diarrhea while others, such as ephedrine, have been associated with fatalities. Individuals who desire to use specific nutritional ergogenics should consult a sports nutrition expert or physician, and also experiment with their use in training before use in compe
Please note that the appropriate language for the citation of this resource
is: The President's Council on Physical Fitness and Sports Research Digest.
The President's Council on Physical Fitness and Sports
The President's Council on Physical Fitness and Sports (PCPFS) was established in 1956 through an Executive Order by President Dwight D. Eisenhower as part of a national campaign to help shape up America's younger generation. Today, the PCPFS serves as an advisory council to the President and Secretary of the Department of Health & Human Services on matters involving physical activity, fitness and sports to enhance and improve the health of Americans of all ages.