Yesterday marked the first day of summer, the time of year we most want to look our best. Personally I need to lose rolls of fat that have turned up on my abdomen and over my shoulder blades. I figure it will take a lot of real hard work on my part and that I'll have to exercise to exhaustion, but certified fitness instructor Stephen Reid said that's not the case.

Mr. Reid is the Spa Director at La Serena at the Reefs, but he's spent more than ten years as a personal trainer in his native London and on cruise ships. He said the most effective way to lose fat is to keep your heart rate in what he calls 'the fat burning zone'.

He has written a book entitled 'Metabolic Fate' that has not yet been published. Over the next few weeks Body & Soul will provide some helpful excerpts from the manuscript. This week we look at how we don't burn fat if we're out of breath.

Long slow distance training, by Stephen Reid

The human body burns fat efficiently at a heart rate of approximately 60 percent of your maximum heart rate. If your heart rate rises over 70 percent of your maximum the fat burning process shuts down entirely, you will not burn any fat at all. No fat, not a bit, none. You'll burn carbohydrates, you might even burn muscle tissue, but you will not burn body fat.

When exercising in your fat burning zone (60 percent of your maximum heart rate) it still takes up to 20 minutes of training for the fat burning process to become properly efficient. Therefore you will not get much fat burning benefit from a 20-minute cardio session. To burn fat efficiently you will need to stay in your fat burning zone for as long as possible, ideally an hour or more.

Once you come out of your fat burning zone it can take another 20 minutes or so to get back in to it should you leave it. For instance if you had been fat burning at the correct heart rate for thirty minutes, then you sprint for five minutes and your heart rate increases, it will be some time before you burn fat efficiently again.

On the bright side, the more you do fat burning cardio the more efficient your body will become at burning fat. Essentially the results will be slower at first but much more dramatic and noticeable the longer you stick with it.

The principle of specificity states that 'The body gets better at what it does, the more frequently it does it'. So if you want to be better at burning fat, do more fat burning cardio.

Suggested cardio sessions are one hour or more of any medium intensity cardio. These workouts are slightly challenging but not exhausting. You can cycle, swim, walk or jog, anything that raises your heart rate to 60 percent of it's maximum and maintains it there.

Check out the website www.trainsmart.com for more information on training to maximize your fat burning potential.