In 1974, the jogging craze was sweeping the United States. Jack Johnstone, a 38-year-old former college swimmer living in San Diego, had started competing in road races as a way of shrinking his “ever-expanding waistline”. Bored by pounding the pavements, he decided to introduce a bit of variety into the sporting calendar.

With friends, he organised a combined swimming, running and cycling race, and advertised it in his local track club newsletter as a triathlon. The entry fee was $1, with prizes for the first five finishers and the proviso that “each participant must bring his own bicycle”.

The event was unheard of - the man engraving the modest trophy had to phone Jack to ask him how to spell triathlon. On the day, September 25, 46 people completed a six-mile run, a five-mile bike ride and 500-yard swim. Little did Jack Johnstone realise that, 26 years later in Sydney, his informal fun run with a swim and bike ride attached would have turned into an Olympic sport.

Thousands of athletes have been attracted by the triathlon’s unique physical and mental challenge - a combination of sporting technique, competition and sheer endurance. Ray Lawrence is one of them. A PE teacher at The Albany School, a comprehensive in Hornchurch, Essex, he had never heard of the triathlon until he went to the US in 1989 as a student to help out on a summer camp scheme for children with disabilities. There he met Dick Hoyt, a former Marine, and his son Rick, who has cerebral palsy.

Dick had been running marathons since 1980, pushing Rick in a wheelchair. Ray was impressed. “Then I discovered he was training for the Ironman triathlon. I didn’t even know what the triathlon was.” First contested in Hawaii in 1978, the Ironman consists of a 2.4- mile swim, a 112-mile bike ride and a 26.2-mile run. Dick was planning to pull his son through the water in a specially-adapted dinghy, cycle with him in a seat on the front of the bike and then push him over the full marathon distance. They finished just within the cut-off time of 17 hours. “He was incredible. I have never met anybody as fit. He was an inspiration.”

Already a keen runner, Ray returned to England and continued to compete in marathons, posting an impressive 2hr:38min in the 1997 Leeds marathon. But long-distance running began to lose its appeal. “You can walk 26 miles in a day if you have to,” he says nonchalantly. “If you are looking for a challenge you have to move on from that.” Munching on a high-energy bar and banana, washed down with herbal tea at his home in Upminster, Essex, Ray attempts to explain what drives him to test his body’s limits. “When you get beyond two hours it is no longer just a swim, bike ride or run. Nutrition is just as important and as difficult as the other aspects. You have to refuel to survive. It is a huge learning curve. Studying and understanding it is difficult.”

Even the most elite athletes cannot store more than about 3,500 calories. In an Iron- man event, most competitors will need about 10,000 calories to get to the finish line. Apart from the physical exertion of swimming the equivalent of 152 lengths of your local pool, cycling from London to Birmingham, then running a full marathon, the race is also a constant fight against dehydration. Ray draws a wavy line across my notebook. That’s bad, he says, pointing to the troughs. Get in too deep a trough and your brain, starved of sugars, tells your body to stop, your legs buckle and you collapse. “It’s a kind of emergency shut-off. Your body tells you when you are in trouble. You can feel it coming on. You get very moody, a lot of negative emotions. Your joints get sore, your legs ge heavy. It takes a lot of unconscious effort to get through it.”

The Olympic triathlon course of a 1,500-metre swim, 42km bike ride and 10km run is a stroll in the park compared to the Ironman. Ray has completed many triathlons, but only one over the Ironman distance, in August last year. It hurt.

“I nearly quit. My back and shoulder-blades locked up after about 50 miles of the bike ride and I stopped eating, which meant I was in trouble. I crawled into the run tent and all I could visualise was the London marathon, thinking I have got to run the London marathon. But I had promised so many people that I would finish. I thought if the worst came to the worst I could walk it.” He smiles at the memory. “In the end I overtook all the people who had gone past me at the end of the cycling.” He finished in just under 11 hours.

In August this year he will do it again, as part of the UK team at the World Long Course Triathlon Championships in Denmark. Soon he will start stepping up the training, putting in about 17 hours a week. It is a punishing 10-week schedule, drawn up with the help of his coach, which peaks a fortnight before the event - with several hours of running, cycling and swimming each day - then slows slightly to conserve energy before race day.

At the bottom of the page, next to the last day he has written “Hooray?” - as if doubting there will be any cause for celebration after all the hard work.

Why put yourself through all that? “A lot of people ask me why I do it. It develops your interest in biology, psychology, physiology. There’s a lot of science involved. Training requires a lot of mental discipline.” But mostly, the way he describes the event makes it sound like a kind of spiritual retreat. “For a day you do nothing but spend 10 to 12 hours absolutely focused on one objective. In our lives we are constantly distracted by events around us. It is rare to get a window of time to focus on something absolutely specific.”

Ray helps to organise a triathlon club for children, Tri Sport Epping, which starts with a 50-metre swim, a 1,600-metre bike ride and a 400-metre run for eight-year-olds and works upwards the older they get. “Before someone can appreciate what you do you have got to educate them in what you do. There is a general lack of knowledge - some people don’t know what a triathlon is. Most kids don’t even know what a mile is. When I teach them, I get them to run a lap of the track. I time them then tell them what the world record is for four times that distance.”

He is evangelical about the benefits (“as a discipline it’s a great alternative to football”) but admits it can be an expensive sport. The bright yellow, lightweight bike hanging from the wall of his study set him back more than pound;1,000, and the specially-adapted wetsuit he uses in competition and for early morning training swims in reservoirs was another couple of hundred pounds. He is trying to get sponsorship towards the costs of competing at his level, which amounts to about pound;2,000 a year.

Ray knows that if he and his wife had children he would have to scale down his obsession. But for the time being, like all good competitors, he is not about to give up. At 31, he knows his endurance will improve throughout his 30s, and he looks to his hero, Dave Scott, the six-times champion of the Hawaii Ironman, who still finished second in 1994 aged 40, for inspiration.

“My ambition is to do the Hawaii Ironman one day. The heat out there is 30, 35 degrees. “My wife has never known any different - which is probably a blessing. But it strengthens our relationship. I am never moody. I love teaching and I love my sport.” Then he corrects himself. “It’s more than just a sport, it’s a lifestyle. And it’s a good lifestyle.”

E-mail Ray Lawrence at: babypig@cwcom.net