A group of fitness fanatics are running through mud, swimming over dams and leaping over fires in a gruelling race designed to challenge both physically and mentally.

Twelve Kiwis are taking on the intense Brisbane Spartan race on April 28 in support of the NZ Heart Foundation for their 50th anniversary.

Organiser Richard Joseph says they set a target of raising a minimum of $5000 for the Heart Foundation, and despite surpassing this total, they plan to keep going.

'With health and fitness being a major part of our lives, the charity relates directly to our way of thinking and we aim to make as much as we can,” says Richard.

Team member Stefan McNeely says they are over the moon with the response and the amount of support they have received.

'You never really know if you are going to make your target,” says Stefan. 'You want to give it a go, but you always question whether you set it too high. It is quite amazing what can happen when you put a bunch of motivated people together.”

He says the team initially started working together at The Gym because they enjoyed the competitiveness. They then found themselves entering in Tough Girl, Tough Guy, Tough Mudder, leading up to their biggest race yet.

The Kiwis will enter the Beast race - one of the three toughest Spartan races, involving a 21km run and more than 40 obstacles.

The team will climb ropes, avoid barbed wire, drag concrete blocks, transverse ropes and throw spears, before facing off against gladiators at the end. On top of that, for each obstacle they fail they will have to do 30 burpees.

'It's regarded as one of the hardest races out there and we have been training really hard and working ourselves up to the challenge,” says Stefan.

'This has been more than just training, it has brought a group of people together who probably would have never met.

'It's been amazing to see how far we have come and we hope to keep going.”