Running might not be the ideal form of exercise, especially if you want to lose weight. Says Greg Brookes, a London-based personal trainer: "Lots of people start running to lose weight and it doesn't always work - and this is why."

"Fat is one of our body's favourite sources of energy," says Brookes. "The more you run, the more your body prepares itself for your next run. You will actually start to hold on to more fat," the Daily Mail quoted him as saying.

Brookes, with a clientele that includes celebrities, high-fliers and housewives, suggests why you won't get leaner is that the body is an amazing machine and will adapt to anything.

"The more time you spend running, the better you become at running and the more efficient you get, the less energy you use and the fewer calories you burn," says Brookes. According to him, running is also bad for joints. "When you run, two-and-a-half times your bodyweight is transmitted through your joints."

"If that force is repeated over and over, eventually your weakest joint will give out. Usually the ankles or the knees are the first to go," he adds.  Contrary to popular belief that any exercise will speed up your metabolism, running can, says Brookes, do the opposite.

NO WEIGHT LOSS

Fat is one of our body's favourite sources of energy. The more you run, the more your body prepares itself for your next run. You will actually start to hold on to more fat: Greg Brookes, personal trainer.