THE vision of professional athletes dead on their feet stumbling over the finish line at the Ironman UK in Bolton on Sunday confirmed my suspicions of this crazy sport.

I say sport, but that doesn’t really do it justice, it’s a personal challenge, not a race.

These days we are used to watching athletes powering over the line in endurance events like the marathon and the Olympic triathlon.

Sports science seems to have stretched the limits of human endeavour so what used to seem on the verge of the impossible is now everyday and mundane.

But seeing the winner, Dan Halksworth, slowly jog through Victoria Square, high-fiving spectators along the way before coming to an unsteady stop on the line and lifting up the tape above his head, reminded me of headier times.

I wasn’t alive, but I’ve seen the footage of Roger Bannister breaking the four-minute mile barrier before falling into the arms of throngs of well-wishers.

Athletes these days do that in their sleep. The world has moved on, so much so that it seems there are very few challenges left to conquer.

Watching the Ironman is like taking a step back into those times of adventurous trailblazers.

It’s clear that, when the pros take to the Ironman course, it’s still not a forgone conclusion that they will finish, never mind break their previous best times.

The second-placed man, Fraser Cartmell, was the pre-race favourite, having won on the event in 2010. Yet he imploded after taking the lead in the marathon, which followed a two-mile swim and a 112-mile bike ride.

After the race he confirmed he had started to be sick as he ran for home, but explained that was par for the course and felt like a winner after refusing to take the easy option and stop.

The true heroes on the day, however, are the “age groupers”, who train for this super-human event while balancing full-time jobs and the pressures of normal family life.

After interviewing a handful of them in the run-up to the event I realised they are wired a little differently.

In a way they are the adventurers of our time in a world where there is very little left to explore.

After watching these men and women cross the finish line after 14 or 15 hours of torture, all I can say is that I feel very comfortable leaving that territory well and truly uncharted.