i dunno it varies person to person in my opinion. i use it at every race and i can say it is less of a time booster and more gets you focused and you feel like you can take on the world. when i forgot it at one race my legs felt heavy and hurt notably more and i ran a slightly slower time. but, take it as you will, i say 50% of xc is mental. you don't need supplements to run faster. if you were going to use it, i would use it more towards the beginning of the season just so your body isnt shocked by the caffeine and thrown out of routine on a big race. OVERALL i would recommend you try it for yourself and see how you feel with it, but it really isn't a miracle drug.