As well as a sore arm, I have managed to injure my lower back too. I'm not quite sure how, but having never really suffered from back pain before, I now know how debilitating it can be.

I did however make it to the gym last night for an hour and did some light bag work and 10-15 minutes on the running machine.

But I'm actually beginning to wonder just how much a part of the weight loss equation exercise actually plays. We are told that a combination of diet and exercise is essential if you want to lose weight, but I'm not convinced.

Now don't get me wrong. Exercise is good for you full stop and benefits both your health and appearance in countless ways.

But does exercise really contribute much to weight loss?

To burn off a pound of weight requires 3,500 calories of energy. Eat 3,500 calories less in a week and you should lose a pound in weight. Simple.

But how much exercise is required to burn 3,500 calories and lose a pound in weight? Much more than you probably imagine.

For example, take me as an example. If I go out running for an hour and manage to cover five miles, not only would it be a miracle in my present physical state (even with a bad back, I doubt I could run five miles) I would burn about 600 calories.

I would need to run for six hours a week and cover 30 miles to burn 3,500 calories.

Or take swimming. Going up and down a pool for an hour at a light to moderate pace would see me burn just over 500 calories. I would need to swim for an hour every day of the week just to lose one pound in weight.

I'd also need to spend an hour a day pedaling away on an exercise bike to burn 3,500 calories in a week.

By contrast, it is extremely easy to consume 500 calories. Eat a Bacon Double Cheeseburger at Burger King and you've done it.

Obviously the heavier you are the more calories you will burn doing any given exercise - and if you are extremely overweight, exercise will contribute more to your weight loss programme.

The other good thing about exercise is that while you're sweating away at your local gym you're not stuffing your face in front of the TV. And anything that takes you away from your food eating comfort zones has to be good.

But when all is said and done, exercise alone will not contribute greatly to your bid to shed the pounds. Watching what you eat will.

PS There is a great tool at myfitnesspal that tells you how many calories you will burn doing a variety of sports.

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