HE MAY be the world champion in aerobics, but Marcus Irwin is hardly a role model for healthy living. Proud possessor of a near-perfect body, Irwin only stays that way by exercising for seven hours a day. A reformed podge, he still enjoys stuffing himself with five croissants laden with strawberry jam and two pieces of toast as a teatime snack. And he hobbles. 'Don't take any notice of my limp. Honestly, aerobics has got much safer since it started in the early '80s. It's just that I went from being a porky blob to world champion in two years - too fast for a body to have to change so dramatically,' he said. Irwin won both the World Aerobics Cup (held in Japan) and the World Aerobics Championships (held in the United States) last year. His mission in Hong Kong was to lecture and give classes to instructors - as well as spread the aerobics gospel. 'Anybody can have a good, toned and slim body by exercising and following a sensible diet,' he said. 'Look at me - after years of being ridiculed and teased about being fat I decided to join a gym. 'It took me weeks to pluck up courage, but I eventually slunk in and started weight training. Three months later, I joined an aerobics class, a few weeks later the instructor didn't show and the class asked me to teach them. 'I remember the aerobics teacher paying me for the class and saying 'one day you'll be a champion'.' Less than two years after starting aerobics he won the 1986 National Aerobics Championships in Australia. But he paid the price. 'In those days aerobics was a whole lot of pounding and other high-impact exercises,' he said. 'Towards the end of 1987, studies were starting to show the damage this was doing to shins, legs, knees and backs.' According to Irwin, many exercises were banned at that time: 'We had to practically re-learn how to teach. Star jumps were out, a lot of abdominal exercises were deemed dangerous for backs, as were straight-legged sit-ups. Aerobics started changing, the pace slowed down and we used a lot more lower impact movements.' Other variations have since been introduced such as step aerobics (exercises based around an elevated platform) and body sculpting (using weights and high-intensity, low-impact exercises) as part of the 'safe' aerobics. According to Irwin, the latest craze in Australia is for slide classes, which may soon be making a debut in Hong Kong. 'You wear foot gear rather like skating boots and slide on a mat with grooves - this is a great exercise for thighs and doesn't entail any jarring,' he said. Hong Kong is, according to Irwin, about five years behind Australia in terms of exercise techniques. 'There hasn't been the international input here we've had in Australia, but from what I see, local instructors are teaching much safer classes,' he said. 'There should, however, be some rule in Hong Kong enforcing that all aerobic instructors are certified, as they are in Australia and other parts of the world.' Moves were afoot to introduce certification in the territory, he said. He recommended aerobics as part of a fitness programme for people who wished to improve their bodies. 'If a person hasn't exercised for years it may be necessary to have a medical check-up, but in all cases it would be advisable to consult a gym instructoror fitness consultant [before] setting up a suitable and safe programme,' he said. 'Aerobics is still a fantastic way of getting fit because it's accessible to the general public and can be fun if there is good music and a vibe. 'It suits a lot of people who think of jogging as going to hell, and wouldn't consider weight-training in a gym. In fact, the hardest part is putting your shoes on and getting there - after that it's easy, you're with other people in the same boat and before you know it, the hour or 40 minutes is up.' He is the first to admit that aerobics isn't some magic way of obtaining great legs. 'The best way of toning the whole body is do a variety of exercises - what we call cross-training; one low-impact aerobics class, one body sculpting class, perhaps a step class, some walking, some cycling, and you'll be doing just fine,' he said. 'Doing four million exercises to improve your legs doesn't work. You need an exercise which will raise your heart rate and burn fat all over your body. Muscle tone comes with regular exercise which means doing something at least three times a week for a minimum of 40 minutes each time.' There are, according to Irwin, three kinds of individual metabolisms, and each group is capable of looking good within their individual limitations. 'There are the burn-in-hell people, the kind who never exercise, eat what they like and always look good,' he said. 'Those who try hard and go through patches of exercising and patches of being couch potatoes and whose weight fluctuates. And those who are obsessive, become hooked on exercise and practically anorexic and then one day get sick of it, relapse completely and become obese. 'No matter which group you are, there is always hope.' His advice: 'Get out there and make a start. Take it easy at first so that you don't burn out. In time you'll get hooked on that great, fit feeling and never want to give it up. That's when good things automatically start happening to your body. Believe me- if I can do it anybody can.'