Caffeine rich coffee is a stimulant. Caffeine stimulates the brain, increasing awareness and concentration.
As the linked article states, Java can stoke your calorie-burning furnace—provided you drink it black. A study in the journal Metabolism found that the caffeine in two cups of coffee may cause a 145-pound woman to expend up to 50 extra calories over the next four hours. "Caffeine stimulates your nervous system, signaling the body to release a small amount of energy from its fat stores," says lead researcher Paul Arciero, Ph.D., an associate professor of exercise science at Skidmore College. "But stirring in milk, cream, or sugar can cause your insulin levels to rise, which diminishes that metabolic effect." www.sparkpeople.com/resource/nutrition_art
However, it should also be noted as this linked article does, that drinking coffee just before a workout might not be the best idea. The Journal of the American College of Cardiology reports that the amount of caffeine in just two cups of coffee limits the body's ability to increase blood flow to the heart during exercise. This is problematic since blood flow to the heart must increase during exercise in order to meet the body's higher demand for oxygen and nutrients. www.sparkpeople.com/resource/fitness_artic
Hope that provides some information of interest.