About 200mg, the effects would be very individual. It would not necessarily give you energy but may make you feel more alter. Also coffee can contain interesting compounds which similar to the ones in chocolate may help blood vessels relax which could also help. I guess this effect lasts for 1-2 hours max
Caffeine is interesting when considered as a sports supplement, its actually the most widely used ergogenic aid in the world!. It increases your bodies ability to breakdown and use fat, increases heart rate, stimulates brain function. I’m not sure how much is in an expresso, but typically the effect of a single dose of caffeine would last a few hours.
I should know the answer to this….being Italian…in addition to Duane and Andy answers….caffeine is also used in some drugs to help the effect of some painkillers or to fight drowsiness….. Taken in small doses can help us in being more alert…but in big quantities can have side effects on the heart and increase blood pressure to much!!!:-(