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I know how I look like. I know how I sound. I know how I walk. I’m just gonna be me. I do me, and you do you.

Caster Semenya

The growing number of transgender and intersex athletes wanting to compete at amateur and elite levels raises complex biological, sociological and ethical issues to which there are no simple answers. Sex testing in women’s sport has been controversial since its introduction in the 1930s. Much of the controversy is fuelled by rumours, misconceptions about motives, a poor understanding of the relevant science and preconceived ideas about fair play.

In this chapter we share data, where they exist, and explore unresolved issues that are the subject of current debate. In complementing the previous chapter on women’s health issues in sport, this chapter helps clinicians understand sex and gender more broadly, in the specific settings of transgender and intersex persons in sport. We will discuss:

  • biology of normal sexual development

  • the genetic basis for sex

  • current definitions of transgender and intersex

  • sex testing in sport and its clinical implications.


To understand sex testing and its effects, it is important to revisit the basics of normal sexual development. When an ovum and a sperm combine to form a zygote, the resulting sexual karyotype is usually XX or XY (the genotype or chromosomal sex). The Y chromosome contains the SRY (sex region of the Y) gene, which ultimately determines a baby’s sex.

The default pathway in human development is for the zygote to develop ovaries, which produce oestrogen and progesterone, eventually leading to a female foetus with female genitalia (Fig 30.1). However, in the presence of the SRY gene, testes develop. If the testes contain functional Leydig cells, the testes produce testosterone, which targets the cells of the external genitalia. The targeted cells only respond if they have functioning androgen receptors, as well as functional 5-alpha-reductase, to convert some of the testosterone into more-active dihydrotestosterone.

Figure 30.1

Normal pathways of male and female sexual development

If all of the above conditions are met, normal primary male sexual development occurs before birth (masculinisation) and around puberty (virilisation), resulting in a male phenotype or somatic sex. If anything goes awry with one of these steps, the baby (foetus) can revert back to the female pathway, resulting in a female phenotype. This explanation is somewhat simplistic, as none of the sex hormones are found exclusively in one sex (i.e. testosterone is not solely a male hormone). However, it represents the relative levels of these hormones and provides a foundation for a basic understanding.


In this section we discuss the basic ...

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