from XTRAMSN:Sport: Fitness: Smell the Coffee

Fitness



Fitness Life
Smell The Coffee
13/02/2004 12:07 PM Fitness Life's Dr Rachel Brown

Many athletes turn to ergogenic aids to optimise their athletic potential. Dr Rachel Brown examines the effects of the one performance-enhancing substance that has stood the test of time: caffeine.

Many competitive athletes are looking for the 'edge' to improve their physical performance. With training schedules and nutrition plans optimised, they may turn to ergogenic aids (substances that enhance physical performance) in an attempt to further their athletic potential. Many of these ergogenic aids come and go with fashion, but one that has remained popular is caffeine. There are numerous anecdotal reports of athletes popping a caffeine pill or drinking a Coke before or during competition to elicit that extra 'kick'. With the widespread use of caffeine and the introduction of caffeine-containing products, it is timely to investigate the potential mechanisms whereby caffeine may aid physical performance. In this regard, it is also important to look at the research conducted to find out whether caffeine has a physiological basis whereby it may improve performance, or whether the performance benefits are purely psychological (in other words, have a placebo effect).

Caffeine is part of the methylxathine family of naturally occurring stimulants found in the leaves, nuts and seeds of a number of plants. Common dietary sources of caffeine include tea, coffee, chocolate, a variety of soft drinks and the increasingly popular energy drinks. Physiologically, caffeine stimulates the central nervous system, cardiac muscle and the release and activity of adrenaline.

So how then might caffeine elicit an ergogenic effect? One of the most popular proposed mechanisms is that by stimulating adrenaline, caffeine mobilises fat, which is an important fuel for the exercising muscle. Theoretically, this would provide an advantage by sparing limited carbohydrate stores in the muscle for intense periods of exercise (such as the final sprint). However, there is limited research to back up these claims and as yet this theory has not been proven. More recent mechanisms have proposed that caffeine increases the mobilisation of calcium within the muscle, which then increases muscle contraction. Caffeine may also influence performance via its effects on the central nervous system, thereby reducing the perception of physical effort or enhancing muscle activity.

Despite not clearly understanding the exact mechanism whereby caffeine may aid performance, there is substantial research that suggests the administration of caffeine will improve physical performance. The performance-enhancing effect of caffeine appears to encompass a variety of sporting pursuits. It has been shown, for example, to increase speed and/or power in simulated race situations. These effects have been prevalent in activities lasting as little as 60 seconds and for exercise exceeding two hours.

There is good evidence to support caffeine as an ergogenic aid for aerobic activity. Most investigators who have examined endurance in situations where fatigue occurs in 30 minutes to two hours, have shown an ergogenic effect. This research has involved a variety of sports such as cycling, swimming and skiing. Caffeine also appears to be beneficial for events lasting only a few minutes, for example, five-minute high-intensity cycling or 2,000-metre rowing. The research for caffeine as an ergogenic aid for events that last only around 90 seconds is less consistent. This is likely due to the fact that performance differences during exercise of short duration are very small and therefore more difficult to measure.

Although most research has looked at the administration of caffeine before exercise, some recent research has also investigated the use of caffeine during exercise. A recent study published in the Journal of Applied Physiology showed that 6mg per kg of caffeine improved time-trial performance at the end of a prolonged cycling bout both in situations where caffeine was ingested one hour prior to exercise or in a series of doses during exercise. This study also formally investigated the popular anecdotal suggestion that drinking 'defizzed' Coke during a race enhances performance. They found that when Coke replaced a sports drink, there was an improvement in performance due to its caffeine and carbohydrate content. This is despite the fact that the Coke provided only 1.5mg per kg of caffeine, which is much smaller than doses associated with ergogenic benefits in the laboratory.

Most studies have shown an ergogenic effect at doses of caffeine ranging from 2 to 9mg per kg, which is equivalent to about 250 to 700mg of caffeine taken one hour or less before an event. The higher doses of 9mg per kg tend to be no more beneficial than lower doses of around 2.5 to 6mg per kg, suggesting that there may be a saturation effect of caffeine as an ergogenic aid. This phenomenon may be important considering that some sporting authorities have banned caffeine as a restricted substance. Intakes of 9mg per kg of caffeine may produce a urinary caffeine level above the International Olympic Committee (IOC) cut-off of 12g per ml. Some sporting bodies have proposed to remove caffeine from the banned substance list.
This whole issue may be somewhat academic when we consider the aforementioned fact that the ergogenic effects of caffeine are seen at intakes far less than would result in a positive doping test. The amount required to produce a positive test is approximately equivalent to about seven cups of coffee ingested one hour before exercise, suggesting that it is highly unlikely that those who have previously tested positive for caffeine have done so unwittingly. People will metabolise caffeine differently and so the amount of caffeine that will elicit a positive doping test will differ from individual to individual. Many studies have shown that urinary caffeine concentrations are extremely variable and a poor reflection of dose and blood caffeine concentrations. However, positive drug test outcomes are unlikely for most individuals on intakes of 5 to 6mg per kg.

A further question is whether prior withdrawal from caffeine may enhance performance even more when caffeine is then reintroduced. The limited data to date suggests that caffeine withdrawal poses no additional benefit and therefore appears unnecessary. Furthermore, the effects of caffeine do not tend to differ between regular caffeine users and non-users.

Are there any potential hazards in taking caffeine? There are some people who do not seem to benefit from the administration of caffeine. They are termed non-responders. Although caffeine intake is relatively safe, there are some individuals who may respond adversely and experience side effects such as tremors, increased heart rate and headaches.

A common claim against the use of caffeine as a performance-enhancing aid is the fact that it is a diuretic (in other words it increases urine production). An increase in urine production during exercise not only increases the risk of dehydration, but is also highly inconvenient. Interestingly though, more recent research has suggested that exercise appears to diminish or eliminate this diuretic effect. Overall, one must be cautious that caffeine is a drug and can affect the central nervous system by causing anxiety, dependency and withdrawal.

There is also the ethical issue over the administration of caffeine because it offers an unfair advantage for athletes. Some experts have reasoned that because caffeine is not a traditional nutrient, athletes who consume it are using it for the express purpose of gaining an advantage. Therefore they have deemed the use of caffeine an act of doping, making it unethical.

Athletes who wish to try caffeine supplementation during competition should firstly experiment during training to find a safe, legal and potential beneficial dose. Because the caffeine content of foods and beverages can vary somewhat, athletes will often use caffeine tablets.