What would be the optimal amount of caffeine intake to improve endurance performance without causing negative side effects, and are there any alternative substances or supplements that could achieve similar benefits without the potential drawbacks of caffeine, such as jitters or an inability to fall asleep after a long ride. How do you think endurance athletes can maximize their caffeine intake to gain a competitive edge, and what role do you think genetics play in determining individual tolerance to caffeine and its effects on performance. Can anyone provide insights on how to measure and track the impact of caffeine on their own endurance performance, and what metrics or key performance indicators would be most relevant in assessing its effectiveness.