Caffeine, without a doubt, is one of the best endurance enhancing supplements and is one of the most widely consumed substances in the world. Whether you get your caffeine from coffee, pre-workout, or pills the end result will be the same. You'll run faster, cycle longer, and fight off fatigue.
There are a few theories behind how caffeine enhances endurance performance. These are:
A meta-analysis done on caffeine and its effects on endurance performance suggest that individuals should consume 3-6mg per kg body weight. The most effective amount will vary from person to person based on habitual caffeine consumption, genetics, body weight, and metabolism. It should be noted that going above 6mg per kg body weight provides no additional benefits and may cause unwanted side effects such as jitters, anxiety, nervousness, and a racing heartbeat.
No, this is largely a myth that came from a poorly run study done in 1960. Research has shown no diuretic effect on those habituated to caffeine. Additionally, in most circumstances, the amount of fluid consumed with caffeine results in net positive hydration (i.e. 12 oz. cup of coffee).
Research has demonstrated that caffeine anhydrous is more effective than the caffeine found naturally in such beverages as coffee or tea.
The answer to this question depends on how you are going to take it. Specifically: