Vitamins that may be helpful

AAKG
AAKG (arginine alpha-ketoglutarate) is a compound made from the amino acid L-arginine and alpha-ketoglutarate (AKG) a substance formed in the body’s energy-generating process. It has been speculated that AAKG may increase production in muscles of nitric oxide, a substance known to have blood-flow-enhancing effects. A double-blind study gave trained weight lifters either 4 grams of AAKG or a placebo three times a day during an eight-week weight-training regimen. AAKG had no effect on body composition but did improve measures of strength and short-term power performance.⁶¹

Creatine
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.^{62 63} Creatine supplementation increases phosphocreatine levels in muscle, especially when accompanied by exercise or carbohydrate intake.^{64 65} 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.⁶⁶

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.^{67 68 69 70 71 72 73} 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.⁷⁴

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,⁷⁵ but one study found no benefit on performance of a military obstacle course run.⁷⁶ Most studies of endurance performance have found no advantage of creatine supplementation, except perhaps for non-weight bearing exercise such as cycling. ^{77 78 79}

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.⁸⁰ Four controlled long-term trials using untrained women,⁸¹ trained men,⁸² or untrained older adults found that creatine improved gains made in strength and lean body mass from weight-training programs.^{83 84}   However, two controlled trials found no advantage of long-term creatine supplementation in weight-training football players.^{85 86}

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.^{87 88} 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.^{89 90 91}

Multivitamin-mineral supplements
Many athletes do not eat an optimal diet, especially when they are trying to control their weight while training strenuously.⁹² These athletes may experience micronutrient deficiencies that, even if marginal, could affect performance or cause health problems.^{93 94 95 96} 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.^{97 98 99}

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.¹⁰⁰ 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.¹⁰¹ The importance of other individual vitamins and minerals is discussed elsewhere in this section.

Antioxidants
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.^{102 103}

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.^{104 105 106} However, taking vitamin C only after such exercise was not effective in another double-blind study.¹⁰⁷ 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,^{108 109 110} several studies have not found such benefits,^{111 112 113 114} 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,¹¹⁵ 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.¹¹⁶

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.^{117 118} Similarly, vitamin E has not benefited exercise performance, ^{119 120} except possibly at high altitudes. ^{121 122}

Alkalinizing agents
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.¹²³ 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.^{124 125 126 127 128 129 130 131 132} 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.^{133 134 135 136 137} Sodium citrate may be preferable to sodium bicarbonate because it causes less gastrointestinal upset.¹³⁸ Another alkalinizing agent, phosphate salts, has been investigated primarily as an endurance performance enhancer, with very inconsistent results.^{139 140}

DHEA
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,¹⁴¹ but 50 mg per day was ineffective in a similar study of elderly men and women.¹⁴² DHEA has not been effective for women or younger men in other studies.^{143 144}

Electrolytes
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.¹⁴⁵ However, the presence of sodium in fluids will often make it easier to drink as well as to retain more fluid.¹⁴⁶ 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.^{147 148}

Glutamine
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.¹⁴⁹ Intense exercise lowers blood levels of glutamine, which can remain persistently low with overtraining.¹⁵⁰ Glutamine supplementation raises levels of growth hormone at an intake of 2 grams per day,¹⁵¹ an effect of interest to some athletes because of the role of growth hormone in stimulating muscle growth,¹⁵² and glutamine, given intravenously, was found to be more effective than other amino acids at helping replenish muscle glycogen after exercise.¹⁵³ 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,^{154 155} 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,^{156 157} 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.¹⁵⁸

Phosphatidylserine
In a double-blind study of active young men, supplementation with 750 of soybean-derived phosphatidylserine per day for 10 days increased the time the men could exercise until exhaustion by approximately 25%.¹⁵⁹ Longer studies are needed to determine whether this effect would persist with continued supplementation.

HMB
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.^{160 161 162 163 164} 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.¹⁶⁵ 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.¹⁶⁶ However, another group of men in the same study given twice as much HMB did not experience any changes in body composition.

Inosine
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.¹⁶⁷ However, three controlled studies demonstrated no beneficial effects on performance and suggested that inosine may impair some aspects of exercise performance.^{168 169 170} Therefore, use of inosine is discouraged.

Iron
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.^{171 172 173} However, anemia in athletes is often not due to iron deficiency and may be a normal adaptation to the stress of exercise.¹⁷⁴ 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,^{175 176 177} though not all,^{178 179} 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.¹⁸⁰

Protein
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.^{181 182 183 184 185} However, long-term controlled trials in young adult men,¹⁸⁶ older men,¹⁸⁷ and women have found no benefits in strength gains from supplementing with amino acids after weight training exercise.¹⁸⁸

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.¹⁸⁹ 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.¹⁹⁰ 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.¹⁹¹ 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.¹⁹² 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).¹⁹³ 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.¹⁹⁴ 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.¹⁹⁵

Pyruvate
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.^{196 197} 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.^{198 199 200} However, in a study of healthy untrained women undergoing an exercise program, supplementing with 5 grams of pyruvate twice a day had no effect on exercise performance.²⁰¹ Studies of pyruvate supplementation on exercise performance in trained athletes have also failed to demonstrate any beneficial effect. Seven grams per day did not improve aerobic exercise performance in cyclists,²⁰² and an average of 15 grams per day did not improve anaerobic performance or body composition in football players.²⁰³ 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.²⁰⁴

Zinc
Exercise increases zinc losses from the human body, and severe zinc deficiency can compromise muscle function.^{205 206} 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.^{207 208} One double-blind trial in women found that 135 mg per day of zinc for two weeks improved one measure of muscle strength.²⁰⁹ 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.²¹⁰ 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.

AKG
AKG (alpha-ketoglutarate) is used by cells during growth and in healing from injuries and other wounds,²¹¹ and is especially important in the healing of muscle tissue.²¹² A controlled study found that intravenous AKG prevented a decline in protein synthesis in the muscles of patients recovering from surgery.^{213 214} For these reasons, it has been speculated that oral AKG supplements might help improve strength or muscle-mass gains by weight lifters, but no research has been done to test this theory.

Arginine/Ornithine
At very high intakes (approximately 250 mg per 2.2 pounds of body weight), the amino acid arginine has increased growth hormone levels,²¹⁵ an effect that has interested body builders due to the role of growth hormone in stimulating muscle growth.²¹⁶ 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.²¹⁷ 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.²¹⁸ High amounts of arginine or ornithine do not appear to raise levels of insulin,^{219 220} 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.^{221 222}

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,²²³ resulted in higher total strength and lean body mass, and reduced evidence of tissue breakdown after only five weeks.²²⁴

Aspartic acid
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.²²⁵ However, most studies have found aspartic acid useless in improving either athletic performance or the body’s response to exercise.^{226 227 228 229 230}

B-complex vitamins
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);²³¹ athletic performance can suffer if these slightly increased needs are not met.²³² However, most athletes obtain enough B vitamins from their diet without supplementation,²³³ and supplementation studies have found no positive effect on performance measures for vitamin B2,^{234 235} vitamin B3 (niacin),²³⁶ or vitamin B6.²³⁷ On the contrary, large amounts of niacin have been shown to impair endurance performance.²³⁸

Beta-sitosterol
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).²³⁹ 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,²⁴⁰ nor do they improve exercise performance or enhance the effects of physical training.^{241 242 243 244 245 246} However, BCAA supplementation may be useful in special situations, such as preventing muscle loss at high altitudes and prolonging endurance performance in the heat.^{247 248} 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.²⁴⁹ Studies by one group of researchers suggest that BCAA supplementation may also improve exercise-induced declines in some aspects of mental functioning.^{250 251 252}

Bromelain
Bromelain is effective for shortening the healing time of such injuries as sprains and strains.²⁵³ 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
Caffeine is present in many popular beverages and appears to have an effect on fat utilization.²⁵⁴ Caffeine does not benefit short-term, high-intensity exercise, according to most,^{255 256} but not all, studies.^{257 258} 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.^{259 260 261 262 263} 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.^{264 265} Effective amounts of caffeine appear to range from 1.4 to 2.7 mg per pound of body weight, taken one hour before exercise.²⁶⁶ 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.²⁶⁷ 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.²⁶⁸

Calcium
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.^{269 270} Contributing to this risk are the diets of these athletes, which are frequently deficient in calcium.²⁷¹ 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
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.^{272 273 274} However, most studies have found little to no effect of chromium on body composition or strength.^{275 276 277 278 279} 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,^{280 281} but the methods used in these studies have been criticized.²⁸²

Chondroitin sulfate
Chondroitin sulfate, 800 to 1,200 mg per day, is effective for reducing joint pain caused by osteoarthritis.^{283 284} Other uses of chondroitin sulfate for sports and fitness, including prevention of joint pain or treatment of sports injuries, have not been studied.

CLA
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.^{285 286} 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.^{287 288 289} 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.²⁹⁰ Further research using more accurate techniques for measuring body composition is needed to confirm these findings.

Coenzyme Q10
Strenuous physical activity lowers blood levels of coenzyme Q10 (CoQ10).²⁹¹ However, the effects of CoQ10 on how the healthy body responds to exercise have been inconsistent, with several studies finding no improvement.^{292 293 294 295} 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.²⁹⁶ 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.^{297 298 299}

Gamma oryzanol
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.³⁰⁰ 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.³⁰¹ 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.³⁰²

Glucosamine
Glucosamine sulfate, 1,500 mg per day, is effective for reducing joint pain caused by osteoarthritis according to most studies.^{303 304 305} 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.^{306 307} Other uses of glucosamine for sports and fitness, including prevention of joint pain or treatment of sports injuries, have not been studied.

L-carnitine
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.³⁰⁸ 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.³⁰⁹ L-carnitine may be effective in certain intense exercise activities leading to exhaustion,³¹⁰ but recent studies have reported that L-carnitine supplementation does not benefit non-exhaustive or even marathon-level endurance exercise,^{311 312} anaerobic performance,³¹³ or lean body mass in weight lifters.³¹⁴

Magnesium
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.^{315 316} Controlled trials suggest that magnesium supplementation might improve some aspects of physiology important to sports performance in some athletes,^{317 318} but controlled and double-blind trials focusing on performance benefits of 212 to 500 mg per day of magnesium have been inconsistent.^{319 320 321 322 323 324} It is possible that magnesium supplementation benefits only those who are deficient or who are not highly trained athletes. ^{325 326}

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.³²⁷ 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).^{328 329} Controlled trials using very large amounts of MCT (approximately 85 grams over two hours) have resulted in both increased and decreased performance,^{330 331} while a double-blind trial found that 60 grams per day of MCT for two weeks had no effect on endurance performance.³³² A controlled study found increased performance when MCTs were added to a 10% carbohydrate solution,³³³ but another study found no advantage of adding MCT,³³⁴ and a third trial actually reported decreased performance with this combination, probably due to gastrointestinal distress, in athletes using MCTs.³³⁵

Octacosanol
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.³³⁶ 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.³³⁷

Ornithine alpha-ketoglutarate
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,^{338 339} no studies on muscle growth in athletes using OKG have been published.

Methoxyisoflavone
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.³⁴⁰ 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.³⁴¹ 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
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,^{342 343} though these deficits are typically replaced within minutes.³⁴⁴ Unpublished reports suggested that ribose supplementation might increase power during short, intense bouts of exercise.^{345 346} 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.³⁴⁷ 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.^{348 349}