Five days feeling total body Delayed Onset Muscle Soreness. Four days rolling IT band syndrome. Three days massaging patellar tendonitis. Two days scrubbing dirty black bog water from between the toes. One day nursing mild hangover. No concussion, but still that was getting off lightly.

There are lots of relaxing ways to spend a weekend in Killarney, and taking part in the Helly Hansen Adventure Race is not one of them. It helps when 2,000 others willingly share in the 69km run-cycle-kayak-cycle-run (although some, sensibly, opt for shorter distances), and there’s no denying that every view along the route is set for stun. But when “whose f***ing bright idea was this?” is the curse of the day then somebody, somewhere has some explaining to do.

Even when blessed with the final blast of our great Indian summer, what unfolded in Killarney last Saturday was not for the faint-hearted – in every meaning of that term. Five hours, 16 minutes, and 52 seconds after setting off from Kate Kearney’s Cottage – without one single pause for breath – I made it to the finish line, over a full hour behind the first man home, Sligo’s Aidan McMoreland, and with no clue what exactly had inspired it all, beyond the old idea that he not busy born is busy dying.

There is always a fresh claim on “the fastest growing sport in the world”, but what is certain is that adventure racing on this mass participation scale hardly existed five years ago. Fáilte Ireland reckons there will be 352 “adventure” events staged here in 2013, two-thirds on the west coast, and most of which attract overseas entries. No wonder Scandinavian brand specialists Helly Hansen are happy to be on board, and among the nine headline adventure races in Ireland (Gaelforce, Achill Roar, Westport Sea-2-Summit, etc), Killarney is now rated as the best.

Nervous silence
We begin shortly after dawn with a quick bus trip, in nervous silence, out to Kate Kearney's Cottage. Out of the starting chute, we run straight up Strickeen mountain, then straight back down, a mere 7.5km, yet more rocky river bed than running trail, freshly watered too after several days of rain. Down at the first transition, the magic blood sugar mix already running low, I take the first snapshot of my fellow adventure racers: mostly male, average age 40, probably working in Web development, and not afraid to spend money on quick-drying adventure gear and expensive carbon-framed bicycles.

Anyway, it’s straight onto the bike for the 35km spin through the Gap of Dunloe and into the Black Valley, the last place in Ireland to get electricity. With damp horse droppings spraying into my face, I pursue a group of five riders, cruising along, when one of them turns around and roars at me for not taking my turn at the front: so much for adventure racing not being a competitive pursuit.

So I drop back and meet Ian Harrington, a Roscommon man, living in Killarney, and 27 years in the Irish Army. In the old days, he and some fellow recruits would run mountain marathons for fun, and finish up with a cycle or swim. “This is certainly an amazing location for an event like this,” he tells me. “You just wonder where it’s all going, or what they’ll come up with next.”

His concern is justified: this week, the New York Times ran an article on the US-based Tough Mudder events, which recently endured its first fatal casualty, when a 28-year-old competitor suffered a full cardiac arrest when plunging from a 15-foot platform into a pool of cold, muddy water. There is the argument that fatal heart attacks like that can and often do happen anywhere, and yet Tough Mudder events actually sell themselves on the promise of dangerous hazards, posting signs at each course that remind competitors, "Remember You Signed a Death Waiver."

This hasn’t stopped Tough Mudder from growing into one of the biggest adventure race brands in the world, their 70 scheduled events in 13 countries this year attracting 700,000 competitors.

Marker on their foreheads
Tough Mudders, by the way, are not identified by race numbers, but a series of numerals written in black permanent marker on their foreheads. The Killarney Adventure Race is not that extreme, not yet anyway, but not everyone will make it to the finish in one piece, even if participant safety is a clear priority.

“This is pure foolishness,” my random partner in the 1.5km kayak tells me, as we all row on, across Muckross Lake, boats against the current. Besides some instant cramping of the hip flexors, this is the easy part, some temporary relief, before we turn and run again straight past Torc Waterfall and up Mangerton Mountain, all 2,750 ft of it.

I happen to pass Séamus Moynihan, running in the opposite direction, framed by the same deep focus and concentration the great Kerry man showed on the football field, and providing the second snapshot of my fellow adventure racers: born competitors, not yet ready to surrender to the dying part.

Mangerton feels more like Calvary, only without the cross, although for sweet consolation there is the constantly expanding vista, out as far as Kenmare Bay, down into Horse’s Glen, and back at Killarney itself, everything in miniature. The summit, for us, is the Devil’s Punch Bowl, another straight turnaround, where a Channel 4 TV crew have strategically positioned themselves to get the best shots of agony disguised as ecstasy.

So to the descent, and with both legs and both arms completely shot, it is classic kamikaze, the more daring the better. Back down by Torc Waterfall, to our bikes, where American tourists in their jaunting cars seem more interested in taking pictures of us than of the lakes, then a gentle ride back to the finish, and a final run into the Gleneagle Hotel.

By then, and for the rest of the day, adventure racing feels less like an adrenaline rush, and more like a slow injection of something else, perhaps more lasting, or even more meaningful. There is no drug testing in adventure racing either, which is a good thing, because in the end, every one of us would test positive for endorphins – and we all know how addictive they are.