In what's slowly becoming known as a tree-athlon, athletes are undertaking a normal triathlon with one key difference: They're carrying large tree stumps on their backs.

British athlete and fitness guru Ross Edgley first attempted the tree-athlon in 2016 in an effort to raise money and awareness for the island of Nevis, for it to become the world's first carbon-neutral island by 2020.

"Nevis is trying to become the world’s first carbon-neutral island," Edgley said in an interview with Redbull. "If Nevis is able to do it I think the ramifications for the rest of the world will be amazing. I also wanted to show how adaptive the human body is – human biology and physiology is amazing and we’re still exploring it. I like the idea that you can just create a weird sport and adapt and train for it. As weird as it sounds, the body will find a way to get through it."