A morning cup of coffee, a mug of tea before bed, an energy shot before a workout or chocolate bar as a treat- all of these items contain caffeine. As it is found in so many food, drink and medicinal products we are all consuming this energy giving stimulant, whether knowingly or not. As a result caffeine is probably the most widely used stimulant in the world.
In the USA, the average caffeine consumption is approximately 200 mg, which is equivalent to 2 cups of coffee, but there are many people globally who have much more than this. In fact, over 10% of the population ingests more than 1000 mg per day.
Caffeine has many effects, but at the end of the day it is a stimulant, and as it is consumed so readily it could be considered the worlds most socially acceptable, legal drug.
There is research that was largely conducted in the 1970’s that suggested that caffeine enhanced endurance performance by increasing the release of adrenaline into the blood stimulating the release of free fatty acids from fat tissue and/or skeletal muscle. The released fat can be used by the working muscles early in exercise. This reduced the need to use muscle glycogen and so more muscle glycogen is available later in exercise to delay fatigue.
More recent research found similar results. It was reported that ingestion of 3-9 mg of caffeine per kilogram (kg) of body weight one hour prior to exercise increased endurance running and cycling performance in the
laboratory. In real life terms- 3 mg per kg body weight equals approximately one mug or 2 regular size cups of coffee, and 9 mg/kg = approximately 3 mugs of 5-6 regular size cups of coffee.
Although this research is great, it should be remembered that coffee and/or caffeine are often reported to be diuretics, suggesting that ingestion of large quantities could lead to poor hydration status prior to and during exercise. So be careful!
For more information have a read of this: http://www.acsm.org/docs/current-comments/caffeineandexercise.pdf