That said, I must caution against the dose suggested in one of the studies Steve mentions. The first study was placebo controlled and used 5 mg/kg as a dose. They found that both recreational and well-trained runner improved their performance by about 1% over placebo. The second study mentions use of a 3g of coffee (150-200 mg caffeine) dose had a similar, modest improvement on performance. I couldn't find the link to the third study Steve mentioned, and I had to go back and listen to make sure I didn't miss something, but they used a 15 mg/kg dose in their trial.
Now, if you are not much of a caffeine user, let me put that in some different terms. I weigh about 180 lbs. divided by 2.2 equals 81 kg. Multiply by 15 mg/kg and my dose for that study would be 1,227 mg of caffeine. If you visit Energyfiend.com you will find an exhaustive list of the caffeine content of various beverages. To participate in this study I would have to drink one of the following:
- 27 Diet Cokes
- 15 Red Bulls
- 7 Grande Cafe Mochas from a popular coffee franchise
- 49 cups of green tea (8 oz.)
- 56 ounces of black coffee
- 16 shots of espresso
Now, I think you can imagine how you might have more energy after a 15 mg/kg dose of caffeine. That said, I drink coffee but I think that might be a bit much for me. Furthermore, remember that the study in question was performed in a controlled environment that presumably had trained professionals monitoring the participants. Which is a good idea because doses like that are enough to induce arrhythmias like atrial fibrillation, which I have seen happen in otherwise healthy young people due to large caffeine doses (and alcohol).
Be safe out there, and always remember to use in moderation!