Studies have shown that consuming 200 to 400 milligrams of caffeine before training or sports competitions can improve performance by up to 20-25 percent. Caffeine is legal in Olympic sports but restricted in sports regulated by the National Collegiate Athletic Association (NCAA). Spanish researchers from the University of Castilla-La Mancha in Toledo found that caffeine improved performance in the bench press and squat when taken in the morning but not the afternoon. Caffeine is an important supplement for improving training intensity. It is more effective for morning than afternoon workouts. Consuming caffeine supplements in the afternoon was less effective and produced more side effects.
Source: Journal of Science and Medicine Sport, published online April 26, 2014