A $100,000 prize is being offered to the man with the fastest sperm in a bizarre new contest that has already attracted more than 10,000 applicants from around the world.
The event - dubbed the Sperm Racing Olympics - will see semen samples from 128 men, each representing a different country, go head-to-head on a microscopic race track in San Francisco next month.
Organisers say the spectacle is designed to shine a spotlight on growing concerns over male fertility, as studies suggest sperm counts have fallen sharply over recent decades.
But despite claims it is the first event of its kind, the same team staged a smaller sperm race in Los Angeles last April when two college students competed live for a $10,000 cash prize.
That earlier contest, held before a crowd of hundreds, featured giant screens, commentary, weigh-ins and live rankings as two university students battled it out under the microscope.
Promoters said it was intended to mix entertainment with awareness around men's reproductive health.
This time, organisers say the stakes are far higher.
Co-founder Shane Fan told the Daily Mail that more than 10,000 men have already applied to compete, including hopefuls from the US, Iran, Israel and even North Korea.
Applicants are now being assessed in a bid to find the 'healthiest' man from each nation before the tournament begins in May.
'We are aiming to find the healthiest person possible for each country to compete,' Fan said. 'There is a lot of work that goes into maintaining a healthy body.'
The selected field will eventually be narrowed to 128 competitors, with one entrant representing each nation. Organisers say the tournament format will mirror mainstream sporting events, with knockout rounds and head-to-head matchups until one overall winner remains.
Competitors will not appear in person. Instead, each athlete will be sent a kit to provide a semen sample, which will then be mailed back to California for testing.
Scientists working with organisers will isolate the sperm before placing them into a specially designed microfluidic track, where they will race in straight-line sprints measuring just 400 microns - roughly 0.02 inches, or about the size of a fine grain of table salt.
Powerful microscopes will magnify every movement and broadcast the action live to viewers online, while giant screens at the venue will show play-by-play progress, stats and leaderboards.
Viewers will also be shown competitors' health data, organisers say, including body composition and biomarkers, allowing fans to choose favourites much like a traditional sporting event.
The sperm crossing the finish line first will be declared the winner - and its owner will collect the six-figure prize.
Fan said previous test races have produced surprising results, with some sperm becoming stuck and taking more than 40 minutes to complete the course.
Others have moved far faster, reflecting the large variation seen between samples.
Initially, each entrant's sperm will reportedly be timed individually. Organisers then plan to group samples by speed before staging direct races between matched competitors, gradually eliminating slower swimmers until the fastest are revealed.
The founders insist the tongue-in-cheek event has a serious purpose.
Research has suggested average sperm counts may have dropped by more than 50 per cent over the last half-century, with obesity, poor diet, inactivity, chronic disease and environmental exposures among factors some scientists have blamed.
Fertility rates have also declined across many developed nations, prompting wider concern about reproductive health and the age at which people are trying to start families.
Doctors assess sperm health not only by number but by motility - how well they swim - because the cells must travel huge relative distances to reach and fertilise an egg.
Poor movement can make conception more difficult even when sperm counts appear normal.
Experts also examine morphology, meaning the shape and structure of sperm, because abnormal forms may be less able to fertilise an egg successfully.
Male fertility can also be affected by smoking, excessive alcohol intake, anabolic steroid use, overheating of the testes, obesity and some medical conditions. In some cases, improving general health can lead to better semen quality over time.
The race's backers say that by turning semen analysis into something shareable and competitive, they hope to remove embarrassment around the topic and encourage more men to get tested earlier.