Both professional football and Olympic athletes are banned from taking ExtenZe because the DHEA in ExtenZe is considered a performance enhancer. To date Viagra has not been banned by these sports agencies. In 2010, 400-meter Olympic gold medalist LaShawn Merritt was banned from competition for taking ExtenZe,  which contains dehydroepiandrosterone (DHEA), a steroid that is banned in athletic competition. Merritt apologized, saying that he did not realize that the formulation contained DHEA. Merritt provisionally accepted a two-year ban from competition, although he announced plans to appeal. Sports authorities, however, were not sympathetic:
The efficiency of human muscle has been measured (in the context of rowing and cycling ) at 18% to 26%. The efficiency is defined as the ratio of mechanical work output to the total metabolic cost, as can be calculated from oxygen consumption. This low efficiency is the result of about 40% efficiency of generating ATP from food energy , losses in converting energy from ATP into mechanical work inside the muscle, and mechanical losses inside the body. The latter two losses are dependent on the type of exercise and the type of muscle fibers being used (fast-twitch or slow-twitch). For an overall efficiency of 20 percent, one watt of mechanical power is equivalent to kcal per hour. For example, one manufacturer of rowing equipment calibrates its rowing ergometer to count burned calories as equal to four times the actual mechanical work, plus 300 kcal per hour,  this amounts to about 20 percent efficiency at 250 watts of mechanical output. The mechanical energy output of a cyclic contraction can depend upon many factors, including activation timing, muscle strain trajectory, and rates of force rise & decay. These can be synthesized experimentally using work loop analysis .