Not sure really......but try this.....I read somewhere that surgeons don't drink caffeine before an operation for fear of their hands shaking........I tried cutting out caffeine for a couple of weeks and noticed that I could play X-box games better, particularly first person shooters where you have to move a gunsight very quickly onto a target with no caffeine in my system......if it works for X-box then it should work on the bike..........
I also think it helps not to be full of caffeine on a trackday, especially if I'm pushing hard to cut a best lap-time as I don't want to be any more nervous than I already am! I also think if you are loaded with caffeine you might over-react slightly when the bike slides, rather than just make a slight adjustment to the throttle......
Each to his own! The guy I ride with also swears by no caffeine either.........bananas and carbs are your best bet for fuel! I don't know if it really makes much difference but we all ride with our little superstitious "routines" and this is one of mine!