In three days time, two of South Pembrokeshire’s famous triathletes, Matthew Evans and Nicky Rees, will be tied together to take to the start line of one of the toughest endurance races in the world.

Without doubt, these local heroes are amongst the most experienced endurance athletes in the country now - the very reason they were awarded their place on the exclusive start line that eludes many. But even for them, this is uncharted territory.

The 11th gruelling Swimrun World Championship, ÖTILLÖ, will be held on Monday, September 5. A total of 120 teams of two are taking on the imposing 75 km race through the archipelago of Stockholm in Sweden. More than 600 teams from all over the world are on the waiting list.

ÖTILLÖ is the original swimrun race and the pioneer for the new and fast growing sport of swimrun. It is one of the toughest one day races in the world. The competitors run and swim for hours on end in wetsuit and shoes, over and between 26 islands in the beautiful Stockholm archipelago, situated in the cold Baltic sea.

Swimrun has grown from being one sole extreme endurance challenge (ÖTILLÖ) to be a true sport with over 200 races around the world in 2016. ÖTILLÖ is the original race, that has a built a mythical reputation in endurance sports circles globally. The 120 teams receive a spot to start, either on merit or through qualifying races. More than 600 teams are on the waiting list.

So how does it work? In swimrun, you alternate trail running and open water swimming. You run in your wetsuit and swim in your shoes. You race in wild nature tied together in teams of two, which is unique and adds to the strong experience and increasing popularity of the sport.

“In today’s society where everything is focused on the individual, the experience is so much stronger when you race with a team-mate. You have to adjust your performance to someone else and you should wisely use your team’s strengths and weaknesses to reach higher. That, together with the beautiful nature experience is why swimrun is so unique and growing in popularity,” said race organiser Michael Lemmel.

Matthew and Nicky will tackle a one-and-a-half marathon run (65 km) on island trails, slippery rocks, unbeaten terrain, in their wetsuit, and 10 km of open water swimming in a cold, sometimes bumpy sea with their running shoes on.

The water is cold, you fight against currents and the course is long. To make it to the finish line before the cut-offs and darkness, you can never stop. If the conditions are right, organisers can probably expect some very fast times, somewhere around over eight hours. But behind the top teams, the majority of the competitors will be struggling for much longer.

Said Matthew: “To be honest, this is the culmination of everything else we have done in the past. The sport of swimrun is new, its getting faster, we are getting older, so our window to have a go at this was getting smaller! There is not a lot of info online about the sport, so you have to learn a lot yourself through trial and error. A bit like it was when we started out in Ironman. And to be fair, with days to go, we are still tweaking.

“I am very lucky to have Nicky as a partner as we do know each other very well, we know it’s going to get dark out there, so being able to be honest with each other from the start is paramount. Being tied together brings an entirely different set of dynamics to the race. We have only done one 60-mile foot race day in the past, that was in the middle of the Sahara, and it was horrendous, albeit with marathons either side! Monday will be what will be and our goal is to cross the line that many do not, with a smile on our faces.

“I am here now and was lucky enough to get a practice swim in. It’s very cold and rippy! It’s like swimming back at home in March! For some reason, I expected it to be warmer! And that’s adventure racing for you; I am sure there will be a huge amount of other surprises out there and that’s what makes it such an amazing sport.”

Nicky added: “To live where we do, this should be our national sport! We are lucky to have been able to put together some quality sessions and we have learnt a lot every single time we have been out. We have had a few funny looks, too, but without doubt this is a sport that is about to fly.

“Strategically, it’s a tough race, too, as you are tied on to your partner, therefore, the swim and run speeds are dictated by each other. If one drops, then it’s all over, so balancing speed with endurance is key. We have raced together all over the world and know each other’s strengths and weaknesses and have a shared many dark and humorous moments, so there will be no polite quips out there; just the traditional one arm slap on the back and go and get this job done.

“We know the cut-offs are tough, it’s almost a fully professional field, so we are going to have to be quick over land where we can. With 56 transitions, just a minute dropped messing with goggles or ropes will cost us an hour overall! It’s the little things like this we have to get right if we are to cross that line on Monday.”

You can follow the lads live online as the race is to be broadcast live, Monday, September 5, from 06:00 CET on http://otilloswimrun.com/live