Sex Testing in Athletics: The Key Cases

Sex classification in athletics has a long and controversial history.

From the exclusion of women in the ancient Olympic Games to today’s hormone‑based regulations, the rules governing who may compete in women’s events have shifted repeatedly in response to scientific developments, legal challenges and public scrutiny.

Women were barred from the first modern Olympics in 1896, but by 1900 Charlotte Cooper became the first female Olympic champion. Limited opportunities led to the creation of the Women’s World Games between 1922 and 1934, and women were finally permitted to compete in athletics and gymnastics at the 1928 Olympics.

Since then, men’s and women’s events have been separated, largely due to research showing that elite male athletes outperform elite female athletes by around ten per cent in strength‑ and endurance‑based events.

Yet the seemingly simple division between men and women has proved anything but straightforward.

The International Association of Athletics Federations (IAAF) has spent decades attempting to define eligibility for women’s events, often with damaging consequences for athletes caught in the system.

What Is Difference of Sexual Development (DSD)?

Most men have XY chromosomes and most women have XX chromosomes, but variations occur. DSD refers to several conditions, including:

• Individuals with XX chromosomes but without a womb and with ambiguous or male‑appearing genitalia

• Individuals with atypical chromosomal patterns, such as X0 or XXY

• Individuals with XY chromosomes, female genitalia and undescended testes, often referred to as “46 XY” or intersex

These variations complicate attempts to classify athletes strictly by sex.

The IAAF’s Current Rules

The IAAF now bases sex classification on testosterone levels, measured in nanomoles per litre (nmol/L).

• Typical male range: 8–30 nmol/L • Typical female range: 0.1–1.8 nmol/L

From 2011, the IAAF set a limit of 10 nmol/L for female eligibility. After legal challenges and new research, the limit was lowered to 5 nmol/L for certain middle‑distance events (400m, 800m, 1500m) in 2018.

Timeline of regulations

• 2011–2015: 10 nmol/L limit

• 2015–2017: Rules suspended

• 2018–present: 5 nmol/L limit for selected events

A Timeline of Key Cases

1966: Nude Parades

In 1966, the IAAF introduced invasive “nude parades,” requiring athletes to undergo visual genital inspections.

Ewa Klobukowska, a Polish sprinter and Olympic medallist, passed this test in 1966 but became the first major casualty of the next regime.

1967–2011: Chromosome Testing

In 1967, Klobukowska failed the new chromosome test and was banned from competition, losing her world records. Chromosome testing continued for decades.

In 1985, Spanish hurdler María José Martínez‑Patiño was disqualified after testing revealed she was intersex. Geneticists later proved she was insensitive to testosterone and gained no athletic advantage from her condition.

Her case exposed the scientific flaws in chromosome testing and pushed the IAAF to reconsider its approach.

2011–2019: Testosterone Testing

The IAAF adopted testosterone testing in 2011.

The rationale was that although intersex individuals make up only 0.00005 per cent of the population, they had won an estimated 8.5 per cent of championship medals in middle‑distance events over 25 years. Testosterone is known to improve endurance, recovery and muscle power, and anabolic steroids used in doping mimic its effects.

Critics argue that testosterone is only one of many biological and environmental factors influencing performance, including heart size, VO2 capacity, coaching quality and training facilities.

Dutee Chand: A Turning Point

In 2014, Indian sprinter Dutee Chand was barred from competing due to naturally high testosterone levels.

She appealed to the Court of Arbitration for Sport (CAS), which ruled in 2015 that the IAAF lacked sufficient evidence that testosterone alone improved female performance.

The ruling forced the IAAF to suspend its regulations and gather new evidence. In 2018, it introduced revised rules targeting middle‑distance events, prompting immediate challenge from South African athlete Caster Semenya.

Caster Semenya’s Case and Why It Matters

Caster Semenya burst onto the world stage by winning the 800m at the 2009 World Championships. Her dramatic improvement led to IAAF investigations into her gender and possible doping.

The process was widely criticised for breaching her privacy, and some South African commentators described it as racist. Semenya withdrew from competition until 2010, when she was allowed to return after hormone treatment.

She went on to win Olympic gold in 2012 and 2016. Between 2015 and 2018 she competed without hormone suppression, but the new DSD regulations threatened her eligibility.

To compete, athletes must:

• Be legally recognised as female or intersex

• Reduce testosterone below 5 nmol/L for six continuous months

• Maintain that level in and out of competition

Semenya argued that the rules:

• Lack a sound scientific basis

• Unfairly discriminate against certain female athletes

• Risk causing serious harm through forced hormone treatment

• Are unnecessary for fair competition

On 1 May 2019, CAS rejected her appeal.

It accepted that the rules were discriminatory but held that the discrimination was “necessary” to preserve the integrity of women’s sport. CAS emphasised that endogenous testosterone is the primary driver of performance differences between men and women.

Semenya briefly won a reprieve from the Swiss Federal Supreme Court, but the court ultimately upheld the CAS decision. She has since joined a South African women’s football club while pursuing further appeals. She has spoken openly about the toll the process has taken, saying it “destroyed” her mentally and physically.

Takeaways

Caster Semenya’s case exposes the deep tension between biology, identity and fairness in sport. It challenges the binary understanding of sex and highlights the need for athletics to recognise that biological traits exist on a spectrum.

Scientific uncertainty remains.

Testosterone is only one factor among many that influence performance, and its relevance varies across sports. Ethical concerns also arise when athletes are asked to take hormone‑suppressing drugs without medical necessity. Semenya herself has said she would never undergo such treatment again.

Finally, the IAAF must improve its protection of athletes’ privacy. The experiences of Semenya, Chand and others show how damaging public scrutiny and leaked medical information can be.

Sex testing in athletics remains one of the most complex and contested issues in modern sport.

The cases that have shaped it reveal not only scientific and legal challenges but also profound questions about fairness, identity and human dignity.