You can consume caffeine from any number of sources, and not just in liquid form. Dark chocolate and a number of fruits contain caffeine. A study published in the International Journal of Sport Nutrition and Exercise Metabolism put one of the most popular caffeinated options to the test on endurance performance.
Comparing the findings of 9 studies where coffee delivering 3 to 8 mg of caffeine per kg of body weight (an average of 325 mg for a 130 pound person) was consumed at least 45 minutes before training, researchers calculated an average increase in performance of 24.2% over non-caffeinated subjects in 5 of these studies. The effect on time trial performance was about 3.1% faster. This was considered moderate evidence of improvement in endurance running or cycling.
