There are many substances advertised and sold to athletes that are legal. Some of them do what is claimed, most of them don't and there are plenty of grey areas. In some cases new substances may come along or old ones get reconsidered as new science comes to light.
I hope below to give you a good idea which supplements are worth considering and which are a waste of your time and money.
Supplements that maybe worth considering
Sports drinks, sports bars, sports gels and cereal bars
These are useful as a convenient way of providing energy for sport. They normally contain too much sugar or salt to be good as meal replacements or snacks between meals, but when consumed during or after exercise they can be very effective at replacing sugars and salts. Try to ensure that the drink, bar or gel that you choose is appropriate for the exercise that you are performing, taking into account the temperature, wind and humidity of your environment. For instance if you sweat a lot you will need to replace more salts, while the harder and longer you exercise for, the more sugars you will require.
Creatine is present in our skeletal muscle in the form of phosphocreatine (PCr). Three functions have been identified for it. The first is the regeneration of the energy molecule, ATP by providing phosphate. This should help fuel all out muscular efforts lasting 5-10 seconds (e.g. sprints). Secondly it can act as a acid buffer during anaerobic exercise. In theory this could assist during efforts involving high lactate levels (e.g. middle distance running). Thirdly it can act as an ATP shuttle during aerobic exercise assisting in continued muscular contractions during steady state exercise.
It sounds like it has widespread potential. However increased levels of PCr are associated with increased water storage and typically a kilo of weight can be put on early on during a PCr loading protocol. This is an important factor that affects its ability to improve performance in weight bearing sports.
PCr loading is best achieved with concurrent ingestion of carbohydrate as this speed the body's ability to store PCr in the muscles. It takes up to a month for the increased muscular PCr levels to diminish to resting levels after finishing a loading protocol.
In practice creatine loading has only proved effective for those doing repeated bouts of short duration intensive efforts. It is not a limiting factor for a first all out attempt however. It comes into its own when PCr stores get depleted after 1-2 maximal efforts. Best usage is for power athletes (e.g. sprinters in training, throwers and jumpers in competition). There are some people who don't appear to respond to PCr supplementation. It is currently thought that about 30% of people fall into this category. It is important to assess it in training before using it for competition.
Creatine supplementation is normally done using 0.07g/kg bodyweight. So a typical 70kg male would supplement 5g daily for a month before a key event. It should be remembered that if muscle mass is less then this amount would be reduced proportionately, so on average women at the same weight would consume slightly less.
Bicarbonate is the most important buffer of excess acidity in our bodies. It can counter the effects of lactic acid accumulation during near maximal intensity efforts of longer than 20-30seconds. It is often taken in the form of bicarbonate of soda (as used in many kitchens for cleaning purposes). Sodium citrate has the same effect. Its effectiveness may be less, but it causes fewer gastrointestinal disturbances than Bicarbonate.
There is a sizeable variation in peoples responses to bicarbonate loading both in the amount of improvement that they show and the size of any side effects. Side effects are not serious, but can include gastro-intestinal distress such as cramping or diarrhoea, which can limit performance benefits. This underlines the importance of conducting trials in training and minor competition before using it for important events.
In practice bicarbonate loading should be effective for events that involve lactate accumulation and this can include events lasting from 30 seconds up to and slightly beyond 1 hour. This includes middle and long distance running, cycle racing and most events in the swimming pool. The best way of using bicarbonate is to load up 1-2 hours in advance of a competition or sporting event. Typical doses for such a loading procedure are 300mg/kg bodyweight, so a 70kg person would ingest 20g of powder with water.
In practice the hyperhydration that can be achieved with glycerol can help with exercise in hot/humid environments, where sweat losses are substantial. It is likely to be most effetive during long endurance events.
Caffeine can be used for both long and short distance events and seems to work by reducing the level of percieved exertion. It used to be a banned substance when found in the blood above a certain level. However now it is legal, firstly because there is a wide range of response by different individuals to the same amount of caffeine ingested, secondly because it maximises its ergogenic benefits at a safe level and thirdly because its use is very widespread. To effectively use caffeine take it about 60 minutes before your race as this allows caffeine levels to peak in your bloodstream. The amount used should be between 1-3mg/kg bodyweight. Thus for a 70kg person it would be around 150mg which equates to one large, strong cup of coffee. If your race is for more than a few hours it will be worth topping up your levels every hour with another 50mg or so.
Supplements with conflicting reports
Carnitine is synthesized in our livers and kidneys from the amino acids, lysine and methionine. It is involved with the transport of fats into our mitochondria (where the fats are oxidised releasing energy in the process). It is suggested that carnitine supplementation could lead to fat loss and help endurance athletes burn fat and spare glycogen reserves. It is also claimed that it could increase maximal oxygen uptake and reduce lacate accumulation during intense exercise.
Chromium is a trace metal that is needed to help the powerful hormone insulin inside our bodies. Insulin helps glucose and amino acids enter into our muscle cells. The amount of chromium in the average diet is thought to be fairly low however, and athletes lose more chromium than sedentary people so it has been suggested by some that supplementation is beneficial for athletes. The benefits touted include fat loss, increased muscle mass and improved glucose metabolism. There is certainly good evidence that chromium supplementation in the form of chromium piccolinate can help those with blood sugar problems, however its ability to help already fit athletes to improve further has not been proven. Chromium is found in brewers yeast as well as nuts, legumes, chocolate, wine and beer and in some fruits and vegetables although not in the sort of amounts (200mcg) found in supplements.
CoQ10 is a fat soluble substance that is an integral part of the provision of energy through aerobic metabolism. It is produced in our livers and also acts as an anti-oxidant protecting our membranes from damage by free radicals. Supplementing Q10 is supposed to improve the health of people with cardiovascular diseases, counter the effects of ageing, improve gum health and improve endurance. There is good evidence that Q10 can help those with cardiovascular diseases and that it can help improve oral health. Evidence for its effects on athletes is equivocal, but this may be due to the age of study subjects and the type of supplementation that has been used.
There is some evidence that CoQ10 can help improve time to exhaustion in graded exercise tests. These improvements have been seen in young subjects (mean age 26), but are likely to be more impressive with older athletes, who will have less CoQ10 in their muscle and heart tissues. The effects of CoQ10 supplementaton on athletic performance appear to be felt fairly quickly. The study results showed improvements both within a few hours and after 2 weeks of regular CoQ10 supplementation(1).
My advice would be to give consideration to CoQ10 supplementation if you are over 40. Vegetarians may have more need of it as the best food sources of CoQ10 include oily fish and organ meats.
Medium chain triglycerides (MCT)
Hydroxy-methyl butyrate (HMB)
Supplements that will waste your time and money
Branched chain amino acids (BCAA)
Glycerol is released during fat burning activities. It is able to increase an athlete's ability to store water when ingested along with sufficient fluid. This water is stored in all the fluid compartments of the body (in cells, blood and plasma).