Chand and several other athletes throughout sports history have failed to qualify to compete in a women's event as a result of their biology. Starting in the 1960s, sex verification tests were done to ensure that only athletes determined to be biologically female could compete as women. That's because in most sports, the top male athletes outcompete the top female athletes by about 10%.

More recently the motivation behind testing has shifted to determining whether an athlete has an "unfair" advantage. Since men typically have more testosterone than women and testosterone is linked to athletic performance, current tests measure female athletes' testosterone levels to ensure they are within a certain range.

Can a test determine an individual's biological sex? And can testosterone produced by an athlete's own body provide an unfair advantage?

pictogram of sprinters

Click on "Human Development" to learn about the development of sex organs and characteristics, including hormone levels.

Human Development

Click on "Case Studies" to explore the sex verification tests that have been used throughout sports history by applying them to two fictitious athletes.

Case Studies


Testosterone is a type of steroid hormone called an androgen. It is produced by the testes in males and by the ovaries in females, and to a lesser extent by the adrenal glands in both sexes. Testosterone can also be taken illicitly by some athletes to increase athletic performance. This interactive focuses on testosterone naturally produced by the body.

Sex verification tests

Tests performed to verify an athlete's biological sex have been referred to as sex-based tests, sex verification tests, gender tests, or gender verification tests (although these tests have to do with biological sex and not gender). They have only been conducted on female athletes in order to qualify them to participate in women's events. More recently these tests have focused more on athletic performance than biological sex.

Biological sex

Biological sex is defined by an individual's combination of chromosomes, hormone levels, internal and external reproductive anatomy, and sex characteristics. It is usually treated as a binary trait: female or male. Biological sex is different from gender, which is based on social and cultural ideas of what it means to be a woman or man. Gender identity refers to an individual's concept of who they are. Gender identity does not always match biological sex.