Caffeine-long article


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Caffeine is one of the most widely consumed drugs in the world and is found in many foods like coffee, tea, soft drinks, and chocolate. There is also a general consensus by sport science investigators that caffeine in some respects is ergogenic. Because caffeine is a drug and has ergogenic properties, sport federations feel a need to control its use by athletes. A problem arises, however, when trying to prevent athletes from using it. Caffeine is a very common chemical in the human diet which makes it difficult to entirely avoid. These considerations force officials to set limits rather than imposing a complete avoidance rule and have classified caffeine under Section II of the IOC doping rules as a restricted drug (positive at > 12 mg/L of urine). The international Olympic Committee (IOC) doping rules say that any athlete with caffeine concentrations greater than 12 milligrams per litre of urine is over the allowable limit. This means, according to a 1995 study by Pasman and colleagues, a person can safely consume as much as 6 mg/kg of caffeine or 420 mg for a 70 kg person and remain under the legal limit (11). In practical terms, four cups (250 ml each) of coffee can be consumed before an event without risk of testing positive. Although drug use in sport is condemned, there appear to be some grey areas in the rules that may be exploited if an athlete wishes to do so.


Structurally related to uric acid, caffeine (1,3,7-trimethylxanthine) is one of three methylated xanthine (pronounced zan-theen) alkaloid derivatives that are present in many plant species throughout the world. The other two methylxanthine derivatives are theophylline and theobromine found in teas and chocolate respectively.

Nearly 100% of caffeine consumed orally is absorbed with peak plasma concentrations occurring 15-120 minutes after an oral dose of about 250 mg. The plasma half-life of caffeine ranges between 3 and 10 hours and is nearly double with the use of oral contraceptives and in habitual users (12). Caffeine is distributed throughout all body water including the brain and the highest concentrations are found in skeletal muscle. Since caffeine concentrations are the highest in muscle tissue, this may be the reason for its ergogenic actions on athletes.

Caffeine is purported to increase work time to exhaustion, decrease lactate levels, reduce the rate of glycogen catabolism, increase free fatty acid mobilization thus inhibiting glycolysis and glucose use, enhance muscle tension and contractile state, facilitate impulse transmissions, increase membrane excitability which may aid in the recruitment of motor units spreading the tension demand over a larger muscle mass, increase tidal volume of the lungs, enhance inspiratory muscle endurance, and lower perceived exertion or sense of effort. All of these effects have not been confirmed, however, and further research is needed before a true understanding of caffeine's actions can be concluded.

Caffeine first came to the athletic world's attention in the late 1960s when power athletes consumed large doses believing it would boost performance. This notion changed when research at the time showed caffeine probably had little effect on anaerobic performance. More recent research, however, has shown that there may be some benefit for power athletes (7,9). Work by Jacobson and colleagues showed caffeine-related strength and power increases and reductions in post-exercise strength loss. The researchers believed that the effect of caffeine on muscle tissue is attributed possibly to a rapid release of calcium ions from the sarcoplasmic reticulum (SR) in muscle, a decrease in the rate of calcium ion uptake, an increase in the calcium ion permeability of the sarcolemma, loss of membrane integrity by rapid dilation of SR tubules, and increased intracellular AMP levels. Without getting into it any further, it simply means that the complex mechanisms of a muscle contraction may be enhanced and become more efficient with caffeine use. There are, however, many studies that show that caffeine has little effect on strength and power (8,17). This area is limited in research and much more is needed before any conclusions can be made whether caffeine is useful for strength and power athletes.

The real excitement involves caffeine and prolonged endurance activity. There is now a general agreement that caffeine can spare both liver and muscle glycogen by facilitating the use of fatty acids for energy (2,3,10,11,13,14,16,17). Unfortunately, there is no agreement on how this is done. Caffeine stimulates the release of catecholamines and cortisol and it was thought that these substances were the main cause of free fatty acid (FFA) release. This theory has since been disproven by research that introduced exogenous catecholamines and cortisol into the body and found that the response was not the same as caffeine's effects.

Some of the research has shown a decrease in perceived exertion or sense of effort by subjects on caffeine. A study by Supinski and colleagues may explain why (13). They looked at caffeine, respiratory muscle endurance, and sense of effort during exercise and found that caffeine augmented inspiratory muscle endurance and decreased the sense of effort. The study did not elucidate the mechanism(s) of the caffeine-augmented inspiratory muscle endurance and the diminished sense of effort but it has been speculated that caffeine may have a central analgesic effect and may enhance neural input to the diaphragm muscle.

A 1987 study demonstrated that a high carbohydrate diet negated the metabolic effects of caffeine during exercise (15). It showed that a combination of "carbohydrate loading" and a high carbohydrate pre-race breakfast inhibited the expected effect of caffeine on lipid mobilization. The investigators postulated that this response was due to increased blood insulin levels present after the high carbohydrate diet and recent carbohydrate ingestion.

However, other researchers have argued that even with an insulin response to carbohydrate ingestion, caffeine can still exhibit an ergogenic effect. They believed caffeine's main effect was on intramuscular triglycerides which were unaffected by plasma insulin. Additionally, most of the studies that showed an ergogenic effect were on athletes who practiced traditionally high carbohydrate diets.

Presently, it is believed that caffeine acts directly on adipose tissue by interacting with receptors and allowing FFA release from the cells. This in turn should increase serum FFA which would feed working muscles and spare glycogen levels. This, however, is not always the case, as some research has shown a glycogen sparing effect but no elevation in serum FFA. It appears that caffeine may enhance the storage of muscle triglycerides at rest and increase the use of these triglycerides during exercise. An interesting study by Essig and coworkers showed that 5 mg/kg caffeine ingested one hour before exercise increased preexercise muscle triglyceride content by 18% compared to controls, which is considerable considering that the caffeine was administered only one hour before (3). How much triglyceride storage would occur after 3 hours? This study also found that subjects used nearly 150% more energy from these increased intramuscular triglyceride stores as compared to controls. Glycogen utilization was reduced by 42% and was speculated by investigators to be due to increased fatty acid use early in the exercise when glucose would have otherwise been used.

It appears that caffeine may have a number of effects that can help spare glycogen including an enhanced preexercise storage of muscle triglycerides, augmented muscle triglyceride use, and increased mobilization of FFA from adipose tissue.

One weakness of the study that investigators admitted to was that a carbohydrate rich diet did not negate the caffeine effects in cyclists because the carbohydrate-sparing effect of caffeine seemed to occur independently of its effect on serum FFA. How can they say that caffeine has no ergogenic effect on their running subjects but it has ergogenic effects on cyclists? These athletes may use different muscle groups but the energy systems are the same. The problem with the research may have been the level of effort the athletes performed at. The athletes ran at 75% of their VO2max which may have caused them to resort to glucose as their main source of energy.

Caffeine has several adverse effects of which the best known is insomnia. Ingestion of caffeine one hour before bed affects the quality of sleep, decreases total sleep time, and reduces stages 3 and 4 of deep sleep (14). These effects combined may cause "pathological sleepiness" during the day. With this in mind, caffeine ingestion should be avoided during the later stages of the day.

It is advised that habitual users of coffee not abstain from caffeine ingestion before an important event because this can precipitate the onset of severe headaches, lethargy, and depression which may be detrimental to performance. In other words, if you are a regular coffee drinker continue to be during competition and training.

Symptoms of restlessness, anxiety, tremors, muscle tension, heart palpitations, and in rare cases, delirium have been documented in naive coffee and caffeine users. It is important that you experiment with caffeine during training or lessor important events to be sure that you can tolerate and benefit from it.

Caffeine can bring on an acid stomach and indigestion in some individuals. This can be minimized if consumed with food. Ingestion of caffeine can also stimulate peristalsis and may cause the urge for a bowel movement. This can be easily remedied by having a movement before training and competition.

One well-known side effect of caffeine is diuresis (secretion of urine). However, the available literature in this area does not support this concept. Two studies reported no changes in core temperature, sweat loss, or plasma volume during exercise following caffeine ingestion (4, 6). Another study demonstrated that caffeine in a fluid replacement drink had no affect on urine volumes and body hydration status during exercise (16). Many will argue that coffee makes them urinate more often and they may be right, but it may be due to increased fluid intake rather than increased caffeine intake. Coffee with nothing added is 98% water, when someone consumes 2-3 cups they may be ingesting 0.5-0.75 litres of water in a short period of time. If the body is adequately hydrated, then this fluid must be eliminated to restore normal water balance, hence the increase in urine output.

It is advised that habitual users of coffee not abstain from caffeine ingestion before an important event because this can precipitate the onset of severe headaches, lethargy, and depression which may be detrimental to performance. In other words, if you are a regular coffee drinker continue to be during competition and training.

Some researchers have suggested that chronic caffeine users will not benefit from caffeine use because these habitual users have developed a tolerance to the drug. This idea has come from evidence showing that chronic caffeine use dulls the catecholamine response to the drug. However, more recent work has shown that habitual caffeine users can benefit from caffeine use during exercise because the primary effect appears, as mentioned, not to be linked to catecholamine stimulation (14). Because caffeine has a number of possible beneficial effects, an athlete may experience maximal results if he/she is caffeine naive, but if this is not possible, an athlete should still be able to greatly benefit from its use.

Keeping the above information in mind, I suggest that athletes who wish to incorporate caffeine in their racing strategy do so slowly and carefully. Athletes should first experiment with caffeine during training to see how it affects them. Only when they are comfortable using caffeine with exercise should they use it during competition.

The best schedule may be to avoid caffeine consumption during the final 4-6 days leading up to an event. This, as mentioned, may not be suitable for habitual users because of the adverse withdrawal effects. In this case, reducing caffeine intake to the minimal tolerance is suggested.

On the day of the event 3 mg/kg of caffeine should be consumed four hours before the event and then another 3 mg/kg one hour before the start. This works out to approximately 200 mg per dose for a 70 kg person for a total of 400 mg. Two cups of coffee at four hours before the start and another 2 cups one hour before racing would be equivalent. This schedule is intended to load the body with caffeine well before the event so that it has time to load the muscle with additional triglycerides. Increased intramuscular triglyceride levels are important because it appears that working muscle has a preference for intramuscular FFA. Early caffeine ingestion is necessary because it takes approximately 1-2 hours for serum caffeine levels to reach their height and it has been shown that caffeine's lipolytic effects (FFA releasing effects) do not peak until 3-4 hours after consumption (10).

For competitions that do not have drug testing, higher doses can be used if desired. The same individual dosages as the above schedule are used but the caffeine is taken at 4 hours pre-event, two hours before, just prior to the start, and for competitions lasting three or more hours, midway through the race. This schedule is necessary to maintain an even caffeine level in the body throughout the pre-race and racing period. A total of 800 mg for a 70 kg person would be ingested on a schedule such as the one above. Research has found that dosages higher than this have no additional benefits (11).

To maximize caffeine's effects it may be useful to avoid carbohydrate ingestion from the three hour period up to race start. As written above, there is evidence that insulin may interfere with some of the beneficial effects by preventing lipolysis (FFA release) and shunting existing serum FFA into fat cells. See this month's "Fat Loss Tip" for more details.

Caffeine use may be most important for athletes competing in events that last more than an hour and because of the nature of the sport, it is difficult to consume food. For example, marathon running, mountain bike racing, cross country skiing, and short to middle distance triathlons. These events all have a ballistic jarring nature to them that prevents many people from consuming adequate food to maintain energy levels. Caffeine will also, of course, be useful in longer events like Ironman distance triathlons, long bicycle road races, and ultra distance running.

Lastly, caffeine levels and it effects may be extended by consuming grapefruit or grapefruit juice (1,5). There is a chemical in grapefruit called naringin that extends the half-life of caffeine. Naringin, which is the substance that gives grapefruit its unique bitter taste, slows the breakdown of caffeine into its metabolite, paraxanthine, in the liver. Consuming canned grapefruit juice is the best strategy because it has much higher concentrations of naringin. The maceration of fresh grapefruit releases the active ingredient which is otherwise locked in (18). This may allow athletes to consume smaller dosages of caffeine and still get the same results and extend the effects later in a long endurance event.

According to the research, it appears that caffeine may be a very useful tool in the enhancement of endurance performance. Many endurance athletes embrace its use but have little understanding why and how caffeine is used. This article was intended to inform athletes of caffeine's applications and leaves the decision for use up to the them.



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16. Wemple, Caffeine ingested in a fluid replacement beverage during prolonged exercise does not cause diuresis. Med. Sci. Sports Exerc. 26:S204, 1994.
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