Humans are actively pursuing superhuman power through technology and scientific experimentation. Athletes have used a variety of ways to increase their performance, including blood doping and the use of anabolic steroids. Bodybuilders have also used drugs to enhance muscle growth and strength. In fact, there are currently people who are using gene therapy to improve their muscular strength. The body's natural ability to produce energy (adenosine triphosphate, or ATP) is limited by its size. The larger your muscles, the more ATP they can make available for use by other cells. However, even a moderately sized muscle group such as that of a bodybuilder can make enough ATP for a large number of cells if it is being used at its maximum capacity throughout the day. Thus, in order to generate more ATP, you need to be working out each muscle group hard enough to reach its maximum potential. This requires a lot of energy! In theory, any human being could become stronger by exercising hard and often. In practice, the human body is not designed for continuous intense exercise; breakaways from normal activity allow our bodies time to repair itself and regain its strength. For this reason, athletes usually supplement their own physical abilities with drug-assisted techniques so that they do not have to exert themselves so hard all the time.