My comment was regarded more towards caffeinated drinks promoted as a way to improve physical endurance. While I agree that caffeine increases focus, by my expe

My comment was regarded more towards caffeinated drinks promoted as a way to improve physical endurance. While I agree that caffeine increases focus, by my experience the increased heart-rate has adverse effects for any hard physical activity or endurance (I do multi-day mountain hiking and alpinism up to 6c grade). By my own experience, drinking a cappuccino just minutes before starting a 1km 30% hill climb will make the effort strenuous on me, and I usually drink 2 espressos a day, which is basically the norm around here. I can easily do the same in less time, walking faster and absolutely no strain if I had at least 3 hours after the cappuccino or don't drink any. In my hiking group this effect has been noted by several other people (we usually go to a bar in the morning before starting the hikes). A redbull for me is already too strong by itself. I think how quickly you can metabolize caffeine is important, but as a rule increasing the hart-rate seems like a dumb idea.