|Creatine monohydrate (for high-intensity, short duration exercise or sports with alternating low- and high-intensity efforts)
Multivitamin-mineral supplements (if deficient)
Vitamin C (to reduce pain and speed muscle strength recovery after intense exercise)
|Citrate (for high-intensity, short- to intermediate-duration exercise)
Creatine monohydrate (for non-weight bearing endurance exercise)
DHEA (for improving strength in older men only)
Electrolyte replacement (for ultra-endurance competition only)
Glutamine (for reducing risk of post-exercise infection only)
HMB (for improving body composition with strength training in untrained people only)
Iron (for iron deficiency only)
Pyruvate (for exercise performance)
Sodium bicarbonate (for performance enhancement in events of specific durations only)
Soy (for exercise recovery only)
Vitamin C (for deficiency only)
Vitamin E (for exercise recovery and high-altitude exercise performance only)
Asian ginseng (for endurance exercise and muscle strength only)
Arginine/Ornithine (for body composition and strength)
Beta-sitosterol/Beta-sitosterol glucoside (in combination for reducing the risk of post-exercise infection)
Branched-chain amino acids (for high altitude and extreme temperature, for reducing the risk of post-exercise infection, or for preventing decline of mental functioning during exercise)
Medium chain triglycerides
Ornithine alpha-ketoglutarate (OKG)
Pyruvate (for improving body composition with strength training in untrained people only)
Cayenne (topical capsaicin)
Reliable and relatively consistent scientific data showing a substantial health benefit.
Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.
Dietary changes that may be helpful for athletic performance
Calorie requirements for athletes depend on the intensity of their training and performance. The athlete who trains to exhaustion on a daily basis needs more fuel than one who performs a milder regimen two or three times per week. Calorie requirements can be as much as 23 to 39 calories per pound of body weight per day for the training athlete who exercises vigorously for several hours per day.2 3 Many athletes compete in sports having weight categories (such as wrestling and boxing), sports that favor small body size (such as gymnastics and horse racing), or sports that may require a specific socially accepted body shape (such as figure skating). These athletes may feel pressured to restrict calories to extreme degrees to gain a competitive edge.4 Excessive calorie restriction can result in chronic fatigue, sleep disturbances, reduced performance, impaired ability for intensive training, and increased vulnerability to injury.5
Carbohydrates are the most efficient fuel for energy production and can also be stored as glycogen in muscle and liver, functioning as a readily available energy source for prolonged, strenuous exercise. For these reasons, carbohydrates may be the most important nutrient for sports performance.6 Depending on training intensity and duration, athletes require up to 4.5 grams of carbohydrates per day per pound of body weight or 60 to 70% of total dietary calories from carbohydrates, whichever is greater.7 8 Emphasizing grains, starchy vegetables, fruits, low-fat dairy products, and carbohydrate-replacement beverages, along with reducing intake of fatty foods, results in a relatively high-carbohydrate diet.
Carbohydrate beverages should be consumed during endurance training or competition (30 to 70 grams of carbohydrate per hour) to help prevent carbohydrate depletion that might otherwise occur near the end of the exercise period. Standard sport drinks containing 6 to 8% carbohydrates can be used during exercise to support both carbohydrate and fluid needs, but these should not contain large amounts of fructose, which can cause gastrointestinal distress.9 At the end of endurance exercise, body carbohydrate stores must be replaced to prepare for the next session. This replacement can be achieved most rapidly if 40 to 60 grams of carbohydrate are consumed right after exercise, repeating this intake every hour for at least five hours after the event.10 High-density carbohydrate beverages containing 20 to 25% carbohydrate are useful for immediate post-exercise repletion.
Adding protein to carbohydrate intake immediately after exercise may be helpful for improving recovery of glycogen (carbohydrate) stores after exercise according to some,11 12 13 though not all,14 15 16 17 18 controlled studies. It appears that adding protein during the post-exercise period is not necessary when carbohydrate intake is high enough (about 0.55 grams per pound of body weight).19
Carbohydrate loading, or “super-compensation,” is a pre-event strategy that improves performance for some endurance athletes.20 21 Carbohydrate-loading can be achieved by consuming a 70% carbohydrate diet (or 4.5 grams per pound of body weight) for three to five days before competition, while gradually reducing training time, and ending with a day of no training while continuing the diet until the event date.
The glycemic index (GI) is a measure of the ability of a food to raise blood sugar levels after it is eaten. Attention to the GI of carbohydrate sources may be helpful for increasing sports performance. Within one hour before exercise, consuming low GI carbohydrates (such as most fruits, pasta, legumes, or rice) provides carbohydrate without triggering a rapid rise in insulin that could result in hypoglycemia and prevent release of energy sources from fat cells.22 Some controlled studies of cycling endurance have found that eating a pre-exercise meal of low-GI foods (lentils, rolled oats, or a combination of low GI foods) is more effective than consuming high-GI foods (potatoes, puffed rice, or a combination of high GI foods),23 24 25 but most studies have found no significant advantage of low GI foods or fructose (a low-GI sugar) compared with other carbohydrate sources in a pre-exercise meal. 26 27 28 29 30 31 32 33 After exercise, on the other hand, high-GI foods and beverages may be most helpful for quickly restoring depleted glycogen stores.34
Protein requirements are often higher for both strength and endurance athletes than for people who are not exercising vigorously; however, the increased food intake needed to supply necessary calories and carbohydrates also supplies extra protein. As long as the diet contains at least 12 to 15% of calories as protein, or up to 0.75 grams per day per pound of body weight, protein supplements are neither necessary, nor likely to be of benefit.35 36 Concerns have been raised that the very high-protein diets sometimes used by body builders could put stress on the kidneys, potentially increasing the risk of kidney disease later in life. A preliminary study of male athletes consuming at least 2.77 grams per pound of body weight per day showed no evidence of kidney impairment; however, the study was limited to one month, and evidence of long-term kidney problems associated with chronic protein loading were not examined.37
Preliminary studies have suggested that increased protein intake may have biological effects that could improve muscle growth resulting from strength training, especially if liquid supplements (typically containing at least 6 grams of protein or amino acids in addition to varying amounts of carbohydrate) are taken either immediately after exercise or just before exercise.38 39 40 41 42 43 44 However, controlled studies have found no advantage of protein supplementation (up to about 100 grams per day or about 14 grams immediately following exercise) for improving strength or body composition as long as the diet already supplies typical amounts of protein and calories.45 46 47
Some athletes have speculated that consuming a high-fat diet for two or more weeks prior to endurance competition might cause the body to shift its fuel utilization toward more abundant fat stores ("fat adaptation").48 However, neither short-term nor long-term use of high-fat diets has been found to improve endurance performance compared with high-carbohydrate diets, and may even be detrimental due to depletion of glycogen stores.49 50
Following a high-fat diet with at least 24 hours of high carbohydrate intake has been suggested as a way to achieve fat adaptation while restoring glycogen levels before endurance competition.51 52 While this concept is supported by physiological studies on athletes, no actual performance enhancement was shown when athletes were tested in competitive situations after a five- to six-day high-fat diet followed by 24 hours of high carbohydrate intake.53 54 55 However, one controlled study found a small, significant benefit of ten days of high fat intake followed by three days of high carbohydrate intake.56
Water is the most abundant substance in the human body and is essential for normal physiological function. Water loss due to sweating during exercise can result in decreased performance and other problems. Fluids should be consumed prior to, during, and after exercise, especially when extreme conditions of climate, exercise intensity, and exercise duration exist.57 Approximately two glasses of fluid should be consumed two hours before exercise and at regular intervals during exercise; fluid should be cool, not cold (59 to 72° F, 15 to 22.2° C). Flavored sports drinks containing electrolytes are not necessary for fluid replacement during brief periods of exercise, but they may be more effective in encouraging the athlete to drink frequently and in larger amounts.58 59
Lifestyle changes that may be helpful for athletic performance
Many athletes use exercise and weight-modifying diets as tools to change their body composition, assuming that a lower percentage of body fat and/or higher lean body mass is desirable in any sport. There is no single standard for body weight and body composition that applies to all types of athletic activities. Different sports, even different roles in the same sport (e.g., running vs. blocking in football), require different body types. These body types are largely determined by genetics. However, within each athlete’s genetic predisposition, variations result from diet and exercise that may affect performance. In general, excess weight is a disadvantage in activities that require quickness and speed. However, brief, intense bursts of power depend partly on muscle size, so this type of activity may favor athletes with greater muscle mass. On the other hand, participants in endurance sports, which require larger energy reserves, should not attempt to lower their body fat so much as to compromise their performance.60
Nutritional supplements that may be helpful for athletic performance
Creatine (creatine monohydrate) is used in muscle tissue for the production of phosphocreatine, a factor in the formation of ATP, the source of energy for muscle contraction and many other functions in the body.61 62 Creatine supplementation increases phosphocreatine levels in muscle, especially when accompanied by exercise or carbohydrate intake.63 64 It may also increase exercise-related gains in lean body mass, though it is unclear how much of these gains represents added muscle tissue and how much is simply water retention.65
Over 40 double-blind or controlled studies have found creatine supplementation (typically 136 mg per pound of body weight per day or 15 to 25 grams per day for five or six days) improves performance of either single or repetitive bouts of short-duration, high-intensity exercise lasting under 30 seconds each.66 67 68 69 70 71 72 Examples of this type of exercise include weightlifting; sprinting by runners, cyclists, or swimmers; and many types of athletic training regimens for speed and power. About 15 studies did not report enhancement by creatine of this type of performance. These have been criticized for their small size and other research design problems, but it is possible that some people, especially elite athletes, are less likely to benefit greatly from creatine supplementation.73
Fewer studies have investigated whether creatine supplementation benefits continuous high- intensity exercise lasting 30 seconds or longer. Five controlled studies have found creatine beneficial for this type of exercise,74 but one study found no benefit on performance of a military obstacle course run.75 Most studies of endurance performance have found no advantage of creatine supplementation, except perhaps for non-weight bearing exercise such as cycling. 76 77 78
Long-term use of creatine supplementation is typically done using smaller daily amounts (2 to 5 grams per day) after an initial loading period of several days with 20 grams per day. Very little research has been done to investigate the exercise performance effects of long-term creatine supplementation. One study reported that long-term creatine supplementation improved sprint performance.79 Four controlled long-term trials using untrained women,80 trained men,81 or untrained older adults found that creatine improved gains made in strength and lean body mass from weight-training programs.82 83 However, two controlled trials found no advantage of long-term creatine supplementation in weight-training football players.84 85
Creatine supplementation appears to increase body weight and lean body mass or fat-free mass, but these measurements do not distinguish between muscle growth and increased water content of muscle.86 87 A few double-blind studies using more specific muscle measurements have been done and found that combining creatine supplementation with strength training over several weeks does produce greater increases in muscle size compared with strength training alone.88 89 90
Many athletes do not eat an optimal diet, especially when they are trying to control their weight while training strenuously.91 These athletes may experience micronutrient deficiencies that, even if marginal, could affect performance or cause health problems.92 93 94 95 However, athletes who receive recommended daily allowances of vitamins and minerals from their diet do not appear to benefit from additional multivitamin-mineral supplements with increased performance.96 97 98
Very little research has been done to evaluate the ergogenic effects of most vitamins or minerals other than those discussed in this article. Supplementation with selenium (180 mcg per day for 10 weeks) had no effect on the results of endurance training in one double-blind trial.99 Vanadyl sulfate, a form of vanadium that may have an insulin-like action, was given to weight-training athletes in a double-blind trial, using 225 mcg per pound of body weight per day, but no effect on body composition was seen after 12 weeks, and effects on strength were inconsistent.100 The importance of other individual vitamins and minerals is discussed elsewhere in this section.
Most research has demonstrated that strenuous exercise increases production of harmful substances called free radicals, which can damage muscle tissue and result in inflammation and muscle soreness. Exercising in cities or smoggy areas also increases exposure to free radicals. Antioxidants, including vitamin C and vitamin E, neutralize free radicals before they can damage the body, so antioxidants may aid in exercise recovery. Regular exercise increases the efficiency of the antioxidant defense system, potentially reducing the amount of supplemental antioxidants that might otherwise be needed for protection. However, at least theoretically, supplements of antioxidant vitamins may be beneficial for older or untrained people or athletes who are undertaking an especially vigorous training protocol or athletic event.101 102
Placebo-controlled research, some of it double-blind, has shown that taking 400 to 3,000 mg of vitamin C per day for several days before and after intense exercise may reduce pain and speed up muscle strength recovery.103 104 105 However, taking vitamin C only after such exercise was not effective in another double-blind study.106 While some research has reported that vitamin E supplementation in the amount of 800 to 1,200 IU per day reduces biochemical measures of free radical activity and muscle damage caused by strenuous exercise,107 108 109 several studies have not found such benefits,110 111 112 113 and no research has investigated the effect of vitamin E on performance-related measures of strenuous exercise recovery. A combination of 90 mg per day of coenzyme Q10 and a very small amount of vitamin E did not produce any protective effects for marathon runners in one double-blind trial,114 while in another double-blind trial a combination of 50 mg per day of zinc and 3 mg per day of copper significantly reduced evidence of post-exercise free radical activity.115
In most well-controlled studies, exercise performance has not been shown to improve following supplementation with vitamin C, unless a deficiency exists, as might occur in athletes with unhealthy or irrational eating patterns.116 117 Similarly, vitamin E has not benefited exercise performance, 118 119 except possibly at high altitudes. 120 121
The use of alkalinizing agents, such as sodium bicarbonate, sodium citrate, and phosphate salts (potassium phosphate, sodium acid phosphate, and tribasic sodium phosphate) to enhance athletic performance is designed to neutralize the acids produced during exercise that may interfere with energy production or muscle contraction.122 Some double-blind studies, though not all, have found that sodium bicarbonate or sodium citrate typically improves exercise performance for events lasting either 1 to10 minutes or 30 to 60 minutes.123 124 125 126 127 128 129 130 131 The amounts used are 115 to 180 mg of sodium bicarbonate or 135 to 225 mg of sodium citrate per pound of body weight. These amounts are dissolved in at least two cups of fluid and are taken either as a single ingestion at least one hour before exercise or divided into smaller amounts and taken over several hours before exercise. Performance during periods of less than one minute or between 10 and 30 minutes is not improved by taking alkalinizing agents.132 133 134 135 136 Sodium citrate may be preferable to sodium bicarbonate because it causes less gastrointestinal upset.137 Another alkalinizing agent, phosphate salts, has been investigated primarily as an endurance performance enhancer, with very inconsistent results.138 139
Dehydroepiandrosterone (DHEA) is a hormone produced by the adrenal glands that is used by the body to make the male sex hormone testosterone. In one double-blind trial, 100 mg per day of DHEA was effective for improving strength in older men,140 but 50 mg per day was ineffective in a similar study of elderly men and women.141 DHEA has not been effective for women or younger men in other studies.142 143
Electrolyte replacement is not as important as water intake in most athletic endeavors. It usually takes several hours of exercise in warm climates before sodium depletion becomes significant and even longer for depletions of potassium, chloride, and magnesium to occur.144 However, the presence of sodium in fluids will often make it easier to drink as well as to retain more fluid.145 Athletes participating in several hours of exercise, especially in hot, humid conditions, should use sodium-containing fluids to reduce the risk of performance-diminishing and possibly dangerous declines in blood sodium levels.146 147
The amino acid glutamine appears to play a role in several aspects of human physiology that might benefit athletes, including their muscle function and immune system.148 Intense exercise lowers blood levels of glutamine, which can remain persistently low with overtraining.149 Glutamine supplementation raises levels of growth hormone at an intake of 2 grams per day,150 an effect of interest to some athletes because of the role of growth hormone in stimulating muscle growth,151 and glutamine, given intravenously, was found to be more effective than other amino acids at helping replenish muscle glycogen after exercise.152 However, glutamine supplementation (30 mg per 2.2 pounds body weight) has not improved performance of short-term, high-intensity exercise such as weightlifting or sprint cycling by trained athletes,153 154 and no studies on endurance performance or muscle growth have been conducted. Although the effects of glutamine supplementation on immune function after exercise have been inconsistent,155 156 double-blind trials giving athletes glutamine (5 grams after intense, prolonged exercise, then again two hours later) reported 81% having no subsequent infection compared with 49% in the placebo group.157
HMB (beta hydroxy-beta-methylbutyrate) is a metabolite (breakdown product) of leucine, one of the essential branched-chain amino acids. Biochemical and animal research show that HMB has a role in protein synthesis and might, therefore, improve muscle growth and overall body composition when given as a supplement. However, double-blind human research suggests that HMB may only be effective when combined with an exercise program in people who are not already highly trained athletes. Double-blind trials found no effect of 3 to 6 grams per day of HMB on body weight, body fat, or overall body composition in weight-training football players or other trained athletes.158 159 160 161 162 However, one double-blind study found that 3 grams per day of HMB increased the amount of body fat lost by 70-year old adults who were participating in a strength-training program for the first time.163 A double-blind study of young men with no strength-training experience reported greater improvements in muscle mass (but not in percentage body fat) when HMB was used in the amount of 17 mg per pound of body weight per day.164 However, another group of men in the same study given twice as much HMB did not experience any changes in body composition.
Inosine is a nucleic acid derivative that appears in exercising muscle tissue. Its role in various cellular functions has led to suggestions that it may have ergogenic effects.165 However, three controlled studies demonstrated no beneficial effects on performance and suggested that inosine may impair some aspects of exercise performance.166 167 168 Therefore, use of inosine is discouraged.
Iron is important for an athlete because it is a component of hemoglobin, which transports oxygen to muscle cells. Some athletes, especially women, do not get enough iron in their diet. In addition, for reasons that are unclear, endurance athletes, such as marathon runners, frequently have low body-iron levels.169 170 171 However, anemia in athletes is often not due to iron deficiency and may be a normal adaptation to the stress of exercise.172 Supplementing with iron is usually unwise unless a deficiency has been diagnosed. People who experience undue fatigue (an early warning sign of iron deficiency) should have their iron status evaluated by a doctor. Athletes who are found to be iron deficient by a physician are typically given 100 mg per day until blood tests indicate they are no longer deficient. Supplementing iron-deficient athletes with 100 to 200 mg per day of iron increased aerobic exercise performance in some,173 174 175 though not all,176 177 double-blind studies. A recent double-blind trial found that iron-deficient women who took 20 mg per day of iron for six weeks were able to perform knee strength exercises for a longer time without muscle fatigue compared with those taking a placebo.178
Certain amino acids, the building blocks for protein, might be ergogenic aids as discussed in this article. However, while athletes have an increased need for protein compared with non-exercising adults, the maximum amount of protein suggested by many researchers—0.75 grams per pound of body weight per day—is already in the diet of most athletes as long as they are not restricting calories. Preliminary studies have suggested that supplementing with combinations of amino acids, typically along with carbohydrate, immediately after exercise increases muscle protein synthesis.179 180 181 182 183 However, long-term controlled trials in young adult men,184 older men,185 and women have found no benefits in strength gains from supplementing with amino acids after weight training exercise.186
In one preliminary study, elderly men participating in a 12-week strength training program took a liquid supplement containing 10 grams of protein (part of which was soy protein), 7 grams of carbohydrate, and 3 grams of fat either immediately following exercise or two hours later.187 Men taking the supplement immediately following exercise experienced significantly greater gains in muscle growth and lean body mass than those supplementing two hours later, but strength gains were no different between the two groups. A controlled study of female gymnasts found that adding 0.45 grams of soy protein (0.45 grams per pound of body weight per day) to a diet that was adequate in protein during a four-month training program did not improve lean body mass compared with a placebo.188 No research has compared different sources of protein to see whether one source, such as soy protein, has a better or more consistent effect on exercise recovery or the results of strength training.
Animal studies suggest that whey protein can increase gains in lean body mass resulting from exercise.189 A controlled trial found that six weeks of strength training while taking 1.2 grams of whey protein per 2.2 of pounds body weight per day resulted in greater gains in lean body mass, but improved only one out of four strength tests.190 Another controlled study found that people taking 20 grams per day of whey protein for three months performed better on a test of short-term intense cycling exercise than people taking a similar amount of milk protein (casein).191 However, a double-blind trial found that men taking 1.5 grams per 2.2 lbs of body weight per day of predigested whey protein for 12 weeks along with a strength training exercise program gained only half as much lean body mass and had significantly smaller increases in strength compared with men using a similar amount of predigested casein along with strength training.192 A controlled study of HIV-infected women found that adding whey protein to strength training exercise was no more effective than exercise alone for increasing strength or improving body composition.193
One group of researchers in two small, controlled trials has reported that 100 grams of a combination of dihydroxyacetone and pyruvate enhanced the endurance of certain muscles in untrained men.194 195 Three controlled studies of untrained individuals using a combination of 6 to 10 grams per day of pyruvate and an exercise program reported greater effects on weight loss and body fat compared with those taking a placebo with the exercise program.196 197 198 However, controlled studies of the effects of supplementation on exercise performance have tested only trained athletes, and these athletes did not experience improvements from pyruvate supplementation. Seven grams per day did not improve aerobic exercise performance in cyclists,199 and an average of 15 grams per day did not improve anaerobic performance or body composition in football players.200 More recently, evidence has appeared casting doubt on the ability of high levels (an average exceeding 15 grams per day depending upon body weight) of pyruvate to improve exercise capacity in a weight-lifting study.201
Exercise increases zinc losses from the human body, and severe zinc deficiency can compromise muscle function.202 203 Athletes who do not eat an optimal diet, especially those who are trying to control their weight or use fad diets while exercising strenuously, may become deficient in zinc to the extent that performance or health is compromised.204 205 One double-blind trial in women found that 135 mg per day of zinc for two weeks improved one measure of muscle strength.206 Whether these women were zinc deficient was not determined in this study. A double-blind study of male athletes with low blood levels of zinc found that 20 mg per day of zinc improved the flexibility of the red blood cells during exercise, which could benefit blood flow to the muscles.207 No other studies of the effects of zinc supplementation in exercising people have been done. A safe amount of zinc for long-term use is 20 to 40 mg per day along with 1 to 2 mg of copper. Higher amounts should be taken only under the supervision of a doctor.
Androstenedione (andro) is a male (androgenic) hormone. It is produced in the adrenal glands and gonads from dehydroepiandrosterone (DHEA) or 17 alpha-hydroxyprogesterone and is converted to testosterone by several tissues, including muscle. One study reported that 100 mg of andro raised testosterone levels in women to six times the normal range and was significantly more effective in this than a similar amount of DHEA.208 A German patent claims that oral andro briefly raises blood levels of testosterone in men.209 One double-blind trial found an initial rise in testosterone in men taking andro, but then a gradual decline to previous levels despite continued supplementation, suggesting that the body may compensate for the effects of andro by decreasing its own natural production of testosterone.210 In controlled studies, andro supplementation at 300 mg per day raised both testosterone and estrogen levels in one trial with men,211 but raised only estrogen in another.212 Lesser amounts of 100 mg per day raised estrogen levels in both of these studies, but had no effect on testosterone levels. Strength and muscle mass gains were measured in one of these studies,213 but no benefit was found from 300 mg per day of andro during an eight-week weight-training regimen. A double-blind trial examining the effect of 200 mg of andro or androstenediol (another male hormone that is converted to testosterone in the body) in older men found no significant changes in testosterone levels at the end of a 12-week, high-intensity weight-training program. Other findings included a lack of measurable advantage of andro supplementation on muscle strength or body composition, increases in estrogen levels, a lowering of HDL (high-density lipoprotein; “good”) cholesterol, and less exercise-induced protection from age-related diseases in men taking andro.214 A combination of related compounds, norandrostenedione and norandrostenediol, given in a total daily amount of 344 mg to strength-trained men for eight weeks, also had no effect on strength or body composition.215
At very high intakes (approximately 250 mg per 2.2 pounds of body weight), the amino acid arginine has increased growth hormone levels,216 an effect that has interested body builders due to the role of growth hormone in stimulating muscle growth.217 However, at lower amounts recommended by some manufacturers (5 grams taken 30 minutes before exercise), arginine failed to increase growth hormone release and may even have impaired the release of growth hormone in younger adults.218 Large quantities (170 mg per 2.2 pounds of body weight per day) of a related amino acid, ornithine, have also raised growth hormone levels in some athletes.219 High amounts of arginine or ornithine do not appear to raise levels of insulin,220 221 another anabolic (bodybuilding) hormone. More modest amounts of a combination of these amino acids have not had measurable effects on any anabolic hormone levels during exercise.222 223
Nonetheless, double-blind trials conducted by one group of researchers, combining weight training with either arginine and ornithine (500 mg of each, twice per day, five times per week) or placebo, found the amino-acid combination produced decreases in body fat,224 resulted in higher total strength and lean body mass, and reduced evidence of tissue breakdown after only five weeks.225
Aspartic acid is a non-essential amino acid that participates in many biochemical reactions relating to energy and protein. Preliminary, though conflicting, animal and human research suggested a role for aspartic acid (in the form of potassium and magnesium aspartate) in reducing fatigue during exercise.226 However, most studies have found aspartic acid useless in improving either athletic performance or the body’s response to exercise.227 228 229 230 231
The B-complex vitamins are important for athletes, because they are needed to produce energy from carbohydrates. Exercisers may have slightly increased requirements for some of the B vitamins, including vitamin B2, vitamin B6, and vitamin B5 (pantothenic acid);232 athletic performance can suffer if these slightly increased needs are not met.233 However, most athletes obtain enough B vitamins from their diet without supplementation,234 and supplementation studies have found no positive effect on performance measures for vitamin B2,235 236 vitamin B3 (niacin),237 or vitamin B6.238 On the contrary, large amounts of niacin have been shown to impair endurance performance.239
Beta-sitosterol, (BSS) a natural sterol found in many plants, has been shown in a double-blind trial to improve immune function in marathon runners when combined with a related substance called B-sitosterol glucoside (BSSG).240 This implies that beta-sitosterol might reduce infections in athletes who engage in intensive exercise, though studies are still needed to prove this. The usual amount of this combination used in research is 20 mg of BSS and 200 mcg of BSSG three times per day.
Branched-chain amino acids
Some research has shown that supplemental branched-chain amino acids (BCAA) (typically 10 to 20 grams per day) do not result in meaningful changes in body composition,241 nor do they improve exercise performance or enhance the effects of physical training.242 243 244 245 246 247 However, BCAA supplementation may be useful in special situations, such as preventing muscle loss at high altitudes and prolonging endurance performance in the heat.248 249 One controlled study gave triathletes 6 grams per day of BCAA for one month before a competition, then 3 grams per day from the day of competition until a week following. Compared with a placebo, BCAA restored depleted glutamine stores and immune factors that occur in elite athletes, and led to a reported one-third fewer symptoms of infection during the period of supplementation.250 Studies by one group of researchers suggest that BCAA supplementation may also improve exercise-induced declines in some aspects of mental functioning.251 252 253
Bromelain is effective for shortening the healing time of such injuries as sprains and strains.254 Typically, two to four tablets or capsules are taken several times per day. Other uses of bromelain for sports and fitness have not been studied.
Caffeine is present in many popular beverages and appears to have an effect on fat utilization.255 Caffeine does not benefit short-term, high-intensity exercise, according to most,256 257 but not all, studies.258 259 However, controlled research, much of it double-blind, has shown that endurance performance lasting at least 30 minutes does appear to be enhanced by caffeine in many athletes.260 261 262 263 264 Inconsistency in reported effectiveness of caffeine in some trials can be explained by differences in caffeine sensitivity among athletes, variable effects of caffeine on different forms of exercise and under different environmental conditions, and effects of other dietary components on the response to caffeine.265 266 Effective amounts of caffeine appear to range from 1.4 to 2.7 mg per pound of body weight, taken one hour before exercise.267 While this amount of caffeine could be obtained in 1 to 3 cups of brewed coffee, most research has used caffeine supplements in capsules, and a recent study found caffeine was not effective when taken as coffee.268 Caffeine consumption is banned by the International Olympic Committee at levels that produce urinary concentrations of 12 mg per milliliter or more. These levels would require ingestion of considerably more than 2.5 mg per pound of body weight, or several cups of coffee, over a short period of time.269
Calcium is important for achieving and maintaining optimum bone density. Some athletes, especially women with low body weight and/or amenorrhea, are at risk for serious bone loss and fractures.270 271 Contributing to this risk are the diets of these athletes, which are frequently deficient in calcium.272 All athletes should try to achieve the recommended intakes of calcium, which are 1,300 mg per day for teenagers and 1,000 mg per day for adults. Other uses of calcium for sports and fitness, including prevention or relief of sports-related muscle cramps, have not been studied.
Chromium, primarily in a form called chromium picolinate, has been studied for its potential role in altering body composition. Preliminary research in animals and humans suggested that chromium picolinate might increase fat loss and lean muscle tissue gain when used with a weight-training program.273 274 275 However, most studies have found little to no effect of chromium on body composition or strength.276 277 278 279 280 One group of researchers has reported significant reductions in body fat in double-blind trials using 200 to 400 mcg per day of chromium for six to twelve weeks in middle-aged adults,281 282 but the methods used in these studies have been criticized.283
Chondroitin sulfate, 800 to 1,200 mg per day, is effective for reducing joint pain caused by osteoarthritis.284 285 Other uses of chondroitin sulfate for sports and fitness, including prevention of joint pain or treatment of sports injuries, have not been studied.
Conjugated linoleic acid (CLA) is a slightly altered form of the essential fatty acid linoleic acid. Animal research suggests an effect of CLA supplementation on reducing body fat.286 287 Controlled human research has reported that 5.6 to 7.2 grams per day of CLA produces only non-significant gains in muscle size and strength in experienced and inexperienced weight-training men.288 289 290 A double-blind study of a group of trained men and women reported reduced body fat in the upper arm after 12 weeks of supplementation with 1.8 grams per day of CLA.291 Further research using more accurate techniques for measuring body composition is needed to confirm these findings.
Strenuous physical activity lowers blood levels of coenzyme Q10 (CoQ10).292 However, the effects of CoQ10 on how the healthy body responds to exercise have been inconsistent, with several studies finding no improvement.293 294 295 296 A few studies, using at least four weeks of CoQ10 supplementation at 60 to 100 mg per day, have reported improvements in measures of work capacity ranging from 3 to 29% in sedentary people and from 4 to 32% in trained athletes.297 However, recent double-blind and/or placebo-controlled trials in trained athletes, using performance measures such as time to exhaustion and total performance, have found either no significant improvement or significantly poorer results in those taking CoQ10.298 299 300
Gamma oryzanol is a mixture of sterols and ferulic acid esters. Despite claims that gamma oryzanol or its components increase testosterone levels, stimulate the release of endorphins, and promote the growth of lean muscle tissue, research has provided little support for these claims and has also shown gamma-oryzanol to be poorly absorbed.301 A recent nine-week, double-blind trial of 500 mg per day of gamma-oryzanol in weight lifters found no benefit compared with placebo in strength performance gains or circulating anabolic hormones.302 However, a small, double-blind trial using 30 mg per day of ferulic acid for eight weeks in trained weight lifters did find significantly more weight gain (though lean body mass was not measured) and increased strength in one of three measures compared with placebo.303
Glucosamine sulfate, 1,500 mg per day, is effective for reducing joint pain caused by osteoarthritis according to most studies.304 305 306 Whether other forms of glucosamine, such as glucosamine hydrochloride, are as effective for joint pain as glucosamine sulfate is unclear at this time, but studies have found some benefits from the use of the hydrochloride form.307 308 Other uses of glucosamine for sports and fitness, including prevention of joint pain or treatment of sports injuries, have not been studied.
L-carnitine, which is normally manufactured by the human body, has been popular as a potential ergogenic aid (i.e., having the ability to increase work capacity), because of its role in the conversion of fat to energy.309 However, while some studies have found that L-carnitine improves certain measures of muscle physiology, research on the effects of 2 to 4 grams of L-carnitine per day on performance have produced inconsistent results.310 L-carnitine may be effective in certain intense exercise activities leading to exhaustion,311 but recent studies have reported that L-carnitine supplementation does not benefit non-exhaustive or even marathon-level endurance exercise,312 313 anaerobic performance,314 or lean body mass in weight lifters.315
Magnesium deficiency can reduce exercise performance and contribute to muscle cramps, but sub-optimal intake does not appear to be a problem among most groups of athletes.316 317 Controlled trials suggest that magnesium supplementation might improve some aspects of physiology important to sports performance in some athletes,318 319 but controlled and double-blind trials focusing on performance benefits of 212 to 500 mg per day of magnesium have been inconsistent.320 321 322 323 324 325 It is possible that magnesium supplementation benefits only those who are deficient or who are not highly trained athletes. 326 327
Medium chain triglycerides
Medium chain triglycerides (MCT) contain a class of fatty acids found only in very small amounts in the diet; they are more rapidly absorbed and burned as energy than are other fats.328 For this reason, athletes have been interested in their use, especially during prolonged endurance exercise. However, no effect on carbohydrate sparing or endurance exercise performance has been shown with moderate amounts of MCT (30 to 45 grams over two to three hours).329 330 Controlled trials using very large amounts of MCT (approximately 85 grams over two hours) have resulted in both increased and decreased performance,331 332 while a double-blind trial found that 60 grams per day of MCT for two weeks had no effect on endurance performance.333 A controlled study found increased performance when MCTs were added to a 10% carbohydrate solution,334 but another study found no advantage of adding MCT,335 and a third trial actually reported decreased performance with this combination, probably due to gastrointestinal distress, in athletes using MCTs.336
Wheat germ oil, which contains a waxy substance known as octacosanol, has been investigated as an ergogenic agent. Preliminary studies have suggested that octacosanol improves endurance, reaction time, and other measures of exercise capacity.337 In another preliminary trial, supplementation with 1 mg per day of octacosanol for eight weeks improved grip strength and visual reaction time, but it had no effect on chest strength, auditory reaction time, or endurance.338
Ornithine alpha-ketoglutarate (OKG) is formed from the amino acids ornithine and glutamine and is believed to facilitate muscle growth by enhancing the body’s release of anabolic hormones. While this effect has been found in studies on hospitalized patients and elderly people,339 340 no studies on muscle growth in athletes using OKG have been published.
Methoxyisoflavone is a member of the family flavonoids (isoflavones). In a U.S. Patent, the developers of this substance claim, based on preliminary animal research, that it possesses anabolic (muscle-building and bone-building) effects without the side effects seen with either androgenic (male) hormones or estrogenic (female) hormones.341 A preliminary controlled trial found that strength-training athletes who took 800 mg per day of methoxyisoflavone for eight weeks experienced a significantly greater reduction in percentage body fat than those who took a placebo.342 Double-blind research is needed to confirm these findings. The U.S. patent also claims methoxyisoflavone reduces appetite and lowers blood cholesterol levels. Whether this claim is true has not yet been demonstrated in published scientific research.
Ribose is a type of sugar used by the body to make the energy-containing substance adenosine triphosphate (ATP). Intense exercise depletes muscle cells of ATP as well as the ATP precursors made from ribose,343 344 though these deficits are typically replaced within minutes.345 Unpublished reports suggested that ribose supplementation might increase power during short, intense bouts of exercise.346 347 However, in a double-blind study, exercisers took four grams of ribose four times per day during a six-day strength-training regimen, and no effects on muscle power or ATP recovery in exercised muscles were found.348 In two other controlled studies, either 10 grams of ribose per day for five days or 8 grams every 12 hours for 36 hours resulted in only minor improvements in some measures of performance during repetitive sprint cycling.349 350
Are there any side effects or interactions with athletic performance?
Refer to the individual supplement for information about any side effects or interactions.
Herbs that may be helpful for athletic performance
Extensive but often poorly designed studies have been conducted on the use of Asian ginseng (Panax ginseng) to improve athletic performance.351 352 While some early controlled studies suggested there might be benefits, several recent double-blind trials have found no significant effects of Asian ginseng on endurance exercise.353 354 355 In many studies, it is possible that ginseng was used in insufficient amounts or for an inadequate length of time; a more effective regimen for enhancing endurance performance may be 2 grams of powdered root per day or 200 to 400 mg per day of an extract standardized for 4% ginsenosides, taken for eight to twelve weeks.356 Short-term intense exercise has also not been helped by Asian ginseng according to double-blind trials,357 358 but one controlled study reported increased pectoral and quadricep muscle strength in non-exercising men and women after taking 1 gram per day of Asian ginseng for six weeks.359 An extract of a related plant, American ginseng (Panax quinquefolius), was found ineffective at improving endurance exercise performance in untrained people after one week’s supplementation in a double-blind study.360
Eleuthero (Eleutherococcus senticosus) supplementation may improve athletic performance, according to preliminary Russian research.361 Other studies have been inconclusive and two recent double-blind studies showed no beneficial effect on endurance performance in trained men.362 363 364 Eleuthero strengthens the immune system and thus might reduce the risk of post-exercise infection. Although some doctors suggest taking 1 to 4 ml (0.2 to 0.8 tsp) of fluid extract of eleuthero three times per day, evidence supporting the use of this herb to enhance athletic performance remains weak.
Arnica-containing ointments are recommended by many practitioners for the treatment of sprains and strains and other traumatic injuries.365 Homeopathic arnica tablets are also used by some practitioners for similar conditions.366 One uncontrolled trial showed that arnica gel applied twice daily reduced symptoms of osteoarthritis of the knee and a double-blind study reported that a combination of topical arnica ointment and oral homeopathic arnica tablets reduced pain in people recovering from hand surgery.367 368 No other studies of topical arnica have been done, but several studies of homeopathic arnica have found it ineffective for treating muscle and joint pain.369 370 371
Cayenne (topical capsaicin)
Capsaicin ointment, applied four times per day over painful joints in the upper or lower limbs, reduces pain caused by osteoarthritis,372 and a plaster containing capsaicin applied to the low back for several hours per day provided relief from chronic low back pain in one study.373 Other uses of cayenne or capsaicin for sports and fitness have not been studied.
Eucalyptus-based rubs have been found to warm muscles in athletes.374 This suggests that eucalyptus may help relieve minor muscle soreness when applied topically, though studies are needed to confirm this possibility.
Guaraná and kola
Some athletes take guaraná during their training; however, there is no scientific research to support this use. Guaraná contains caffeine. Another caffeine-containing herb sometimes used during training is kola nut.
Extracts of Tribulus terrestris (puncture vine) have been reported in preliminary studies to affect anabolic hormones in men.375 However, a double-blind trial found no effect of 1.5 mg per day of tribulus per pound of body weight on improving body composition or strength performance results from an eight-week strength training program.376
The ability of yohimbine, a chemical found in yohimbe bark, to stimulate the nervous system,377 378 promote the release of fat from fat cells,379 380 and affect the cardiovascular system 381 has led to claims that yohimbe might help athletic performance or improve body composition. However, a double-blind study of men who were not dieting reported no effect of up to 43 mg per day of yohimbine on weight or body composition after six months.382 No research has tested yohimbe herb for effects on body composition, and no human research has investigated the ability of yohimbine or yohimbe to affect athletic performance. Other studies have determined that a safe daily amount of yohimbine is 15 to 30 mg.383 However, people with kidney disorders should not take yohimbe, and side effects of nausea, dizziness, or nervousness may occur that necessitate reducing or stopping yohimbe supplementation.
Are there any side effects or interactions with athletic performance?
Refer to the individual herb for information about any side effects or interactions.