Warren Hawke is enveloped by fatigue. His joints are throbbing and his muscles aching. "It's sort of swine flu without the flu so just swine, Isuppose," he muses, stifling a yawn. The symptoms are, at least, a distraction from the screaming pain in one of his knees, the legacy of an extensive football career with Sunderland, Morton and Queen of the South on a 38-year-old body.

It is a tale of woe familiar to his footballing contemporaries but particularly pertinent to Hawke, given how he will spend this weekend. On Sunday morning hewill join around 1300 competing in the Antwerp Half-Ironman, an epic endurance event comprising a 1.2mile swim, followed by 56 miles on a bike and culminating in a half-marathon.

A standard Sabbath it is not.

"I'll be painkillered and ibuprofened out of my face but I'llmake it," insists the Englishman, who attributes the illness to a combination of heavy training and a seven-month old baby causing disturbed sleeping patterns. "Theswim and cycle are fine but a couple of miles into the run I'll start to feel it and end up crossing the line like a zombie. But it will all be worth it."

As well as the obvious personal satisfaction that will come from completing the course, Hawke is hoping to help those, like his father-in-law, who are living with cancer by raising around £2000 for Maggie's Centres. It is something he has been keen to do ever since his playing days ended and he began working with the PFA, but believed that his athletic background made asking people to sponsor him for marathons unfair.

"They are huge challenges but Ialways felt that there wasn't too much of a transition for someone like me, who was used to training," he explains. "Iwas picking up injuries from running so Idecided to get a bike, which Ienjoyed, and Ialways liked swimming so it made sense to try a couple of triathlons and combine all three. You hear about these Ironman events and it just got my interest, so Idecided to do this one as a stepping-stone to a full one in the next couple of years."

Despite only beginning running to avoid another post-football legacy - the bulge - it is scant surprise his ambition has expanded instead of his stomach. Hawke admits to being the kind of person who requires a target to train for, and initially competed in half-marathons before quickly progressing to the full version, but found himself unfilled by either. He believes he is not alone, a fact that explains a recent surge in participants in triathlon, with a fitter populace finding that they want to explore their boundaries in increasingly challenging ways.

This weekend's event, albeit only' a half-Ironman, will do just that. "This really is outside the comfort zone," he says. "I'm experiencing every feeling possible - excitement, fear, apprehension, doubt - everything is there. There are so many things you have to worry about, right down to whether you have enough Vaseline, but Ithink my biggest concern has always been the nutrition: I've never had to worry about refuelling during an event before but to go six or seven hours you need to take on something like 120g of carbohydrates every hour. Ican only imagine how bad it would be ina 12-14 hour race."

If Sunday goes well, he might notneed to imagine. With some of the shorter distances, Hawke thought that once it was over it would be out of his system, but he has discovered that he is, in fact, an addict. Next week, he will sit down and analyse his race, look at what he could improve, where he could have gone quicker and what he could have done differently. Theconstant quest for improvement feeds the compulsion, just as in his earlier career.

"It's a substitute for the football ina way and that is one of the things that scares me the most," Hawke reveals. "Iam very, very competitive and Iworry that I'll go too quickly in the swim or start off too fast on the bike and find I've nothing left in the tank because that's always been the way Iam, trying to do my best in everything Ido. So I'm going to have to learn to say to myself, hold on, just slow down, take your time, it's a long distance' and just pace myself.

"It's going to be difficult, probably the most difficult thing I've done and Isometimes think would it really be that bad to have a bulge? But Iknow I've got to do it for the charity, despite the fact Ifeel pretty rotten. The swim and cycling will be fine but I'll just have to drag my arse around the 13 miles of the run."