Caffeine has long been recognized as a performance-enhancing drug. It’s been proven to increase endurance, decrease perceived effort, and increase oxygen uptake, all of which adds up to a maximum improvement in time trial performance of about 3.4 percent. In fact, before the 2000 Olympics, the International Olympic Committee banned excessive use of caffeine as a performance enhancing substance. (Excessive equaling 12mg per liter of urine, or about eight cups of coffee.) The World Anti-Doping Agency overturned that ban in 2004, but WADA still monitors caffeine use in elite athletes “in order to detect patterns of misuse in sport,” according to the agency's website.
Abstaining from taking in caffeine before your race may, indeed, make the ergogenic substance more effective. A review of 21 studies on the effects of caffeine on endurance performance found that cutting out caffeine for at least seven days before using it at an event will give an athlete the greatest chance of optimizing its effects.
Another study found that people who consume less than 50mg of caffeine—or half a cup of brewed coffee—per day experienced greater performance enhancement than people who consume 300 or more milligrams of caffeine per day, which suggests cutting back on your intake, or abstaining completely, will help you get the most out of caffeine on race day.
As for when and how much you should take in, a new study suggests that consuming six milligrams of caffeine per kilogram of body weight one hour before racing results in the greatest performance improvements. However, because everyone metabolizes caffeine differently, studies have suggested that the optimal dose lies somewhere between 3 and 6mg/kg of body weight, or 204 to 408mg—two or three cups of coffee—for a person weighing 150 pounds.
Note that one study showed that although taking in 6mg/kg one hour before you start to exercise is optimal, taking in 1mg/kg of caffeine every 20 minutes during a two-hour time trial enhanced performance just about as well. Even taking in as little as 1.5mg/kg during the last 40 minutes of a two-hour time trial, the study suggests, can effectively enhance endurance performance.
The bottom line: Caffeine can be an effective—and legal—performance enhancer. Abstaining from caffeine for the week leading up to your event, and consuming 6mg of caffeine per kg of body weight one hour before you race may be the most effective way to reap its benefits.