AS the CEO of the Kiss Gyms empire, Rupert Mackenzie Hill knows a thing or two about keeping fit and setting himself a challenge.

But this week the 52-year-old will take on a test of epic proportions by completing a gruelling triathlon that only 24 people in the entire world have ever completed.

Kicked off by running 87 miles from London to Dover, the Enduroman triathlon then asks brave competitors to take a dip in the Channel to swim 21 miles before cycling to the iconic Arc de Triomphe in Paris.

And while Rupert is no stranger to facing intrepid challenges, having previously trekked across the Sahara desert, he is still anxious about how he'll make it to the finishing line in France in light of testing weather conditions.

"I did the last challenge with a bunch of strangers and because there was such a big build up to it, afterwards we wanted to do something together again.

“Someone in the group came up with this idea but one-by-one, everyone else has dropped out and I’m the last one left so I thought why not do it solo?

“I’ve done triathlons before so I thought if it is possible for a middle-aged bloke to have a go then why not. Saying that, I completely underestimated how difficult it is to swim that distance in the channel and my knees have been knocking together at thinking about it."

The Enduroman triathlon was created almost twenty years ago and over that time, hundreds have attempted to tackle the challenge.

The dad-of-three started training earlier this year and while he hasn’t managed to clock many laps in the pool, he did go on a swimming camp in Spain to help him with the triathlon.

“I realised I can’t swim very well from going to Spain," Rupert joked. "I thought I could swim quickly as a kid but it is like asking a 100m sprinter to run a marathon. I found a great book about swimming and that has given me a lot to work on and now I’ve been able to get faster and faster.

“Most people who try to take it on fail at different stages and a few lucky ones have completed it.

"Where it is quite difficult is that you are tired before you swim and a lot of the people who take part are mega athletes so out of the five doing it this year, I will be the only amateur one."

Rupert, who is ex-military, will be supported by a number of people in his challenge and his progress will be documented on social media - much to the delight of his colleagues at Kiss Gym in the town as many gave him advice on keeping his stamina up during the gruelling run, swim and cycle.

“There are two things that I think I will take from my military experience and that is persistence and not giving up.

"I've had lots of tips from the fantastic personal trainers we have at each of the three sites of Kiss Gyms who have given me help on the endurance side of it.

“From training I have found that if you can get into a rhythm and massively focus on what you’re doing then you can get into a state of flow and weirdly it makes time go.”