If you are afraid to exercise because you think that after you stop, your muscles turn to fat, you are out-of-shape for the wrong reason.

Saying that your muscles can turn into fat is like saying that diamonds can turn into glass. Muscle and fat are two different types of tissue on your body! You simply cannot turn muscle into fat, or fat into muscle.

When you exercise, your muscles become larger and stronger because exercise causes extra protein building blocks, called amino acids, to deposit in muscles. All day long, amino acids pass from your muscles into your bloodstream and then back into muscles, with exercise as the major stimulus to force amino acids back into muscles.

When you decide to go off your weight training program or take a break from the gym, you start losing a little bit of muscle due to the sudden inactivity (which is perfectly normal). This also tends to lower your metabolism.

With your muscles getting smaller your metabolic rate will also reduce so that whereas before you were easily able to burn off the calories, you no longer can as the size of your muscle directly affects your metabolic rate. You are also not needing as much energy so a lot of the food you are taking on is not needed any more. When the body has surplus energy, in the form of food that it does not need, it will store it as fat.

When you stop exercising, fewer amino acids go back into muscles and they become smaller. Amino acids that do not go back into muscles, are picked up by your liver. Since your body has no way to store extra protein, your liver uses them for energy or converts them into fat. Most people would also almost always neglect their diet as well when they take a break from the gym. So if you stop exercising, you have to eat less or you will become fat, but muscles never turn into fat.

Associate Professor Lynch: Muscle and fat are two different things. Muscle is designed to contract, pulling on tendons, which move our bones and give our bodies movement. Fat on the other hand, is the body's way of storing energy. The less energy we use, the more fat we store, ready for when we need it.

So what happens when you stop exercising?

"When we're exercising heavily, we're working our muscles hard, we're eating a lot of food usually to fuel those workouts. If we stop exercising and we're still eating the same amount of food, quite naturally the energy balance between energy in, as food, and energy out, as exercise, or energy expenditure, changes. And so the idea is the balance shifts towards increasing body fat," says Associate Professor Lynch.

In most cases, when you stop training, your appetite won't stop. So if you were training really hard to get in shape, do yourself a favour and continue with diet, so you will at least protect yourself from gaining fat as you will already lose some of your muscles.

Bad eating habits + a lower metabolism + lower muscle mass all add up in the long run and will make it seem as if the person's muscle is being turned into fat - while in reality, what is actually happening is that precious muscle is being lost and fat is being accumulated.