Caffeine increases core temperature, which can be detrimental to endurance activities.

“caffeine's a really interesting thing to talk about I'm like intrigued by that one because that was one of the things that when it came on board it was like oh there's no going back like I couldn't imagine doing a race without caffeine and yet like people have such different experiences with it and uh you know I've learned from like science recently how it does like increase your core temperature which is kind of detrimental to endurance activities but the thing that's interesting is like that I I understand the science behind that but that just hasn't been my experience at all like I am 100% faster with caffeine on board than without caffeine on board and I've tried both ways”