Testosterone is a steroid molecule synthesized in the gonads of both men and women (by the Leydig cells of the testes and by the ovaries, respectively), and is secreted by the adrenal cortex in response to LSH and FSH secretion from the anterior pituitary gland in order to stimulate the development of secondary male sex characteristics, such as increased bone density, libido and muscle strength.

Its proliferation into the world of international competition as a performance-enhancing drug is well-documented — in 2006, American Olympic Sprinter Justin Gatlin was banned from competition after confirmation of his testosterone usage, and in 2013 former professional cyclist Lance Armstrong admitted to utilizing testosterone, as well as EPO (a hormone naturally produced by the kidneys to stimulate the production of red blood cells) in order to maximize oxygen input to the muscles during intense physical activity.

In order to combat the pervading rise of performance-enhancing drugs in international competition, the International Association of Athletics Federations (IAAF) developed strict guidelines to promote what they claim to be the sanctity of fair and open competition. Part of their plan entailed setting a limit on the number of testosterone women who were competing were allowed to have in circulation, with levels above five nanomoles per liter being deemed ineligible for competition without hormone treatment.

This ruling has the potential to harm the competitive capability of a plethora of athletes with naturally high levels of testosterone, such as South African Olympic 800m Champion Caster Seymana, who has filed a case against the IAAF for banning her from competition for over a year due to her above-average testosterone levels.

While the IAAF's rationale behind their decision appears sound at face value, medical professionals have deemed the guidelines as "unscientific" and without merit. Dr. Sheree Bekker from the University of Bath, as well as Professor Cara Tannenbaum from the University of Montreal, have claimed that serum testosterone levels alone cannot define biological sex or physical function, and that such a hastily-made resolution could have far-reaching implications for future generations of athletes with natural physiology that could be perceived as a genetic advantage.

They argue that testosterone levels are just one indicator of sports performance that does not factor in a wide variety of conditions, and they take issue with an analysis commissioned by the IAAF that attempted to identify the causation between high levels of testosterone and performance in a sport since these results could not be independently reproduced. The decisions made regarding such a crucial aspect of fair competition in international competitions such as the Olympics and the Diamond League will have significant impacts on the manner in which athletes will be deemed eligible for competition for many years to come.