Caffeine and Performance in Endurance Sports

In an article titled Caffeine As an Ergogenic Aid (Current Sports Medicine Reports Volume 5(4), August 2006, p 215–219) Brian Keisler MD and Thomas Armsey MD review the effects of caffeine in endurance performance. Many studies explore caffeine use as a performance enhancing substance. Most of these agree, at appropriate dosages, caffeine can increase time to fatigue as well as decrease time to finish.
For fans of coffee, however, the beverage is a two edged sword. In the first place, regular coffee drinkers will experience less improvement of performance compared to non-coffee drinkers. In the second place, studies show no performance gain with caffeine administered by way of coffee. Apparently, coffee contains substances that compromise the ergogenic effect of caffeine. The majority of studies performed used caffeine administered in capsules. No studies, however, have looked at the affects of caffeinated energy gels.
The dosages at which caffeine benefits athletic performance outpace those found in most gels and sports drinks. The benefits start at 250 mg and continue until 600 mg. Most studies do not go beyond 600 mg. For comparison, a 7.5 oz cup of coffee provides 100 mg and most gels provide between 25 and 50 mg of caffeine. Interestingly, to provide benefit, the athlete can divide the total does of caffeine into smaller doses taken throughout the race. The affects can be seen up to 6 hours after ingestion. Caffeine is considered legal by the International Olympic Committee in dosages below 800 mg which, theoretically, allows the athlete to benefit from the substance while staying withing the guidelines.
The article concludes by giving a summary of the above findings and a note of caution: "Caffeine is a commonly used substance that can be ingested in many different forms. It has a variety of different physiologic effects throughout the body. It is a relatively benign substance but can produce some adverse effects on blood pressure with long-term, consistent usage."