Sports nutritionists are studying the positive effects of small amounts of caffeine on athletes. A dose of five milligrams per kilogram of body weight seems to improve endurance by reducing glucose burning and increasing fat burning. Caffeine spares glucose, which is in limited supply in the body, both as glucose and glycogen. Caffeine-containing beverages like unsweetened coffee, tea or diet cola beverages have also be used in research studies. I would not recommend using caffeine for glucose sparing until the word is in from researchers because of the potential for serious side effects of caffeinism.
Individual tolerance does vary according to caffeine sensitivity.
If not, even a small dose would cause you significant nervousness. The International Olympic Committee has banned the use of caffeine in their competitions. Also, it may impair hand steadiness, which may be a concern for some athletes.