Last updated on .From the section Sport

CrossFit was created by former gymnast, Greg Glassman

The quest to find the fittest athletes on the planet has begun.

Over the next five weeks, hundreds of thousands of athletes of all ages and abilities will push their fitness to the limit to try to reach next August's CrossFit Games in Madison, Wisconsin.

It is billed as the "largest fitness competition on earth" but fewer than 250 competitors will reach the finals.

What is CrossFit?

An exercise regime which develops strength and fitness and was created by American Greg Glassman.

There are 15,000 CrossFit gyms across more than 160 counties.

Each day participants get a different workout - never the same as the last - which consists of a number of set exercises which are high intensity and designed to improve all-round fitness.

Who can compete?

CrossFit bills itself as "where grassroots meets greatness".

On Thursday, the Open started. It's one of three ways to qualify for the CrossFit Games - and is open for anyone aged over 14 to enter.

A new workout is released every Thursday, which participants complete either in a gym or at home and post their scores online.

The workouts tests "cardiovascular/respiratory endurance, stamina, strength, flexibility, power, co-ordination, agility, balance, and accuracy."

The top 20 athletes around the world, and the first-placed male and female competitors from each country, will qualify for the Games.

Following the Open, top age-group athletes from 14-17 and 35-60 and over have a second online qualifier to earn an age-group spot in the finals, and competitors can also qualify by winning sanctioned events known as 'Sanctionals'.

The CrossFit Games

The season culminates with the Games - said to be the "world's premier test to find the fittest on Earth" with prize money of $1.6m (£1.2m) on offer.

It is claimed the Games were created to "fill a void" as "no other true test of fitness existed".

Over four days, athletes will be scored on a number of demanding workouts, with no prior knowledge of the challenges that lie ahead.

Though anyone can take part, winning is another matter.

Tia-Clair Toomey is undefeated in the women's competition since 2017, and just so happens to be the 2018 Commonwealth Games weightlifting champion.

American Mat Fraser has been the men's champion for the past four years.

Britain's best hope in recent years has been Samantha Briggs - the former fire-fighter is a full-time CrossFit athlete and was the women's world champion in 2013.