The ergogenic potential of caffeine is not exactly a recent phenomenon. Indeed, there is documentation to suggest that it has been used to enhance performance for more than 30 years. However, with caffeine having been removed from the banned list of the International Association of Athletics Federations (IAAF) earlier this year, now may be a good time to revisit the topic.

Caffeine is found naturally in coffee beans, tea leaves, chocolate, cocoa beans and cola nuts, and is often added to carbonated drinks. This makes it one of the most widely consumed behaviourally-active substances in the world. For most of us, caffeine provides a stimulus for concentration or waking up. For athletes, however, it can be used to prolong endurance exercise and enhance power production.

Initial studies examining the effect of caffeine supplementation on endurance performance reported a 21-minute improvement in time to exhaustion while cycling at 80% of VO₂max⁽¹⁾. Similarly, elite distance runners who consumed 10mg of caffeine per kg of body mass immediately before a treadmill run to exhaustion significantly improved their performance by 1.9% compared with controls⁽²⁾.

In another study, competent distance swimmers consumed caffeine (6mg per kg of body mass) 2.5 hours before swimming 1500m and found that their split times improved significantly for each 500m of the swim, while average swim times were 1.9% faster than when carried out without the aid of caffeine⁽³⁾.

A study on endurance cyclists looked at the effect on time to exhaustion of pre-exercise administration of each of the following⁽⁴⁾:

• 5mg caffeine per kg body mass;
• 9mg/kg caffeine;
• 13mg/kg caffeine;
• placebo.

In a test carried out at 80% of their maximal power output, all the caffeine-supplemented cyclists showed a 24% improvement in time to exhaustion. However, no greater benefits were apparent with doses of caffeine higher than 5mg per kg of body mass.

The ergogenic effect of caffeine on endurance performance has also been demonstrated with aerobic exercise performed at high ambient temperatures⁽⁵⁾. And performance benefits have also been demonstrated during short duration, high intensity exercise in rowers⁽⁶⁾.

However, when the effects of caffeine ingestion on sprint or power performance are examined, the ergogenic benefits are less clear, with several studies showing no improvement. Nevertheless, competitive swimmers have demonstrated improvements in sprint times of 2 and 4% following caffeine ingestion (250mg) for two 100m sprints separated by 20 minutes⁽⁷⁾. And a further study has demonstrated a 7% improvement in power performance during a series of six-second Wingate sprints⁽⁸⁾.

Sprint and power performance

Research evidence on the effects of caffeine ingestion on sprint and power performance is limited and inconclusive by comparison with the large volume supporting its use with endurance athletes. And any beneficial effects on power performance are likely to be most marked in trained athletes.

A precise explanation for the ergogenic effects of caffeine remains elusive. It is likely that the enhancement in endurance capacity results from caffeine’s ability to facilitate the use of fat as an exercise fuel, thus sparing the body’s limited carbohydrate reserve. Caffeine’s facilitating effect on neuromuscular activity is thought to be responsible for any improvement in short duration, high intensity exercise.

Irrespective of the mode of exercise, many research subjects have reported lower levels of perceived exertion and localised muscular fatigue following caffeine ingestion, which will undoubtedly have boosted their performance capacity.

It would be remiss not to mention at this stage that athletes who normally avoid caffeine may experience adverse effects if they start using it as an ergogenic aid. Many of these side effects are well known and include anxiety, gastrointestinal disturbances, restlessness, insomnia, tremors and heart arrhythmias. The scientific literature suggests that the risk of such side effects is increased if caffeine is taken in doses higher than 9mg per kg of body mass.

In addition, caffeine can act as a diuretic, which could lead to an unnecessary pre-exercise loss of fluid, with negative knock-on effects on thermal balance and exercise performance, particularly in hot environments. However, this diuretic effect is reduced when caffeine is consumed during exercise, which helps to explain why some athletes rely on defizzed cola during events.

The ergogenic effects of caffeine vary greatly, but are most predictable in trained athletes.

Athletes should also be aware that beneficial effects do not occur consistently in habitual caffeine users, suggesting a level of ‘caffeine tolerance’. One way round this may be for caffeine users to shun all caffeinated foods and drinks for a period of 4-6 days prior to pre-event supplementation in order to optimise its benefits.

The role of nutrition

Nutritional status may also account, in part, for the observed variation in responsiveness to caffeine, since athletes who normally consume high-carbohydrate diets may demonstrate a blunted fat mobilisation effect.

Individual differences in caffeine sensitivity, tolerance, and hormonal response may also impact on caffeine’s ergogenic effects. Additionally, research has shown that the potential ergogenic effects of caffeine taken in the form of coffee are lower than when taken as a capsule with water. It is also advisable to consume additional fluid to offset the diuretic effects of caffeine when it is taken prior to exercise.

In summary then, small amounts of caffeine (as little as contained in one mug of coffee) have been shown to have a favourable impact on factors like decision-making and reaction time, while larger amounts (equal to 2-3mg per kg of body mass) have been shown to enhance exercise performance, particularly endurance.

Dosages higher than 5mg per kg of body mass do not appear to elicit any greater performance effects; furthermore, they tend to raise the risk of unwanted side effects.

Caffeine is absorbed rapidly, with peak plasma concentration reached in around one hour. It also clears from the body fairly rapidly, taking about 3-6 hours for blood caffeine concentrations to decrease by one half.

As with any intervention, individual responses will vary, and athletes would be well advised to rehearse their caffeine dosage strategy thoroughly before putting it to the test in a key event.

Andrew Harrison

References

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