Athletes who use caffeine before exercising or competition may be upgrading themselves more than they realize. Caffeine is classified as a stimulant and is the most commonly used drug in the world. Caffeine has the same affects that amphetamines and cocaine have, just to a lesser degree. Caffeine crosses the membranes of all the body's tissues. It can exert effects on the central nervous system and the peripheral tissues that result in physiological effects. Studies have shown that caffeine improves performance in a variety of different activities. This stimulant has been shown to be a powerful ergogenic aid that is beneficial in athletic training and performance. Caffeine has been found to increase speed and power, improve the length of training, and assist the athlete in resisting fatigue. Caffeine has been found to stimulate the brain, which contributes to clearer thinking and ability to concentrate more intensely on the task at hand. Studies have shown that up to 25% of athlete's ages 11-18 years old have used caffeine in an effort to increase their athletic performances. Because of caffeine's effect on the body and its ability to increase an athlete's performance, Olympic Committees have debated on whether caffeine should be tested before the Olympic Games.