Consuming caffeine before training can lead to vasoconstriction and reduced performance in individuals not accustomed to it.

“Now, caffeine is a bit of a complicated one. I talked about this on a podcast long ago, but I'll just remind you that it turns out that if you are caffeine adapted, in other words, if you are used to drinking caffeine then the ingestion of caffeine, most often will cause vasodilation who actually allow more blood flow through. However, if you are not caffeine adapted, it will cause vasoconstriction due to an increased stress response.”