Scientists have been studying the effect of caffeine on athletic performance for quite some time. Based on the evidence that exists, the American College of Sports Medicine (ACSM) currently reports that 3 to 9 milligrams of caffeine per kilogram of body weight can improve endurance athletic performance (lasting up to 2 hours) and short-term, intense exercise (lasting about 5 minutes).
Body weight = 150 lbs
150 lbs / 2.2 = 68.2 kgs
68.2kgs X 3 mg caffeine = 204.6
68.2kgs X 9 mg caffeine = 613.8
So a person who weighs 150 pounds would need between 205 mg and 614 mg of caffeine. A cup of coffee has at least 100 mg of caffeine.
Studies have shown that caffeine can help to increase power output and speed. Unfortunately, studies cannot confirm that caffeine in the form of coffee will elicit the same results because caffeine was administered in pill form. Fortunately, caffeine does not cause dehydration as commonly thought.
Practical advice: If you are using gels or sports drinks with caffeine in them, know that they are safe and they may even improve your performance. Do not ever try something new on race day! Do not overdo the caffeine. By that, I mean that more is not always better. Be sensible, do not take so much caffeine that you are jittery, and don't expect this to help you win the race. Train, train, train!