It's a question that been hotly debated over the years, but a lot of people still believe 20 minutes is the magic number as far as they're concerned, that's when the fat starts peeling off.
When we exercise, there are two energy sources carbohydrates, also known as sugars, or fats. But which one actually determines a greater weight loss? And how long do we need to exercise for to start seeing the benefits?
Reporter Leila McKinnon has offered to work up a sweat to find out.
Dr Thomas Allison is a specialist researcher in the area of cardiovascular fitness. He works at the world-renowned Mayo Clinic in the US state of Minnesota. And he's devised a test to answer this 20-minute exercise question.
Leila hops on a treadmill and straps on the necessary equipment to get the 30-minute test underway. To make sure she stays in top shape throughout the test, the doctor will monitor Leila's heart rate. And by also measuring the amount of oxygen she consumes, he'll be able to tell whether she's burning fats or sugars through measuring Leila's carbon dioxide levels.
Dr Allison wants to see how Leila fares at different exercise levels, so she'll start off walking, followed by a run. When Leila has stopped exercising, Dr Allison will monitor whether or not she is burning fat.
If we're to believe the oft quoted theory, Leila won't start burning fat for at least 20 minutes.
Immediately after the test Leila switches from a hard run to a gentle walk as a cool-down routine and guess what? She's burning fat and calories.
"You're going to continue burning calories for the next five, 10, 15 and 20 minutes while your body cools down from this exercise," says Dr Allison.
He adds that we're burning fat the moment we start walking and we don't have to do it for 20 minutes for our bodies to benefit.
"For light exercise, the body can afford to choose an inefficient fuel like fat."
However, once you pick up the exercise intensity, things change. "As exercise becomes more intense, we need a more efficient fuel that will burn more quickly, produce more energy and require less oxygen and so we shift over to glucose," he says.
Glucose or fat, the net result either way is that you're still burning calories and the more calories you burn, the more weight you'll lose.
The 20-minute, fat-burning theory is not true. You start burning fat before 20 minutes of exercise. In fact, you can start burning fat from the moment you start exercising.
As most of us don't have hours and hours of time on our hands, we might as well make optimal use of our workout time by doing relatively high intensity exercise.
Dr Allyson's advice? Hard physical workouts like swimming, cycling or climbing will always beat easy workouts like walking. This doesn't mean going crazy and exercising till you drop, rather, do relatively high intensity level exercise so that when you're finished you're not exhausted, but somehow tired. It will take your body longer to recover from that exercise so that throughout the recovery period you'll continue to burn calories.
So why are we losing the battle of the bulge?
Obesity is a major issue around the world and that's due in large part to the kinds of foods we're eating. Let's take a moment to examine the impact a banana split would have on your exercise routine.
"You can't stay at the gym long enough to overcome a banana split," says Dr Allison.
"To burn off the calories that you can eat in 10 minutes with a big bowl of ice-cream with nuts and fruit and syrup on it, you would have to exercise vigorously for two hours or more. If you don't control the dietary intake, almost any amount of exercise is insufficient to lose weight and maintain a healthy weight."
It's not just banana splits we're talking about here. You'd need to lift weights for three hours to burn off a cheeseburger, ride a bike for 90 minutes to see off a muffin and play tennis for two hours to burn a couple of slices of pepperoni pizza.
If you're serious about getting fit and losing weight, the time to start is now.
In general, the more calories you put in, the more you're going to have to burn in order to lose weight. Regular exercise really does help. So try not to spend too much time in those armchairs, get out, get active and reap the rewards!
- Are you one of those people who think if you do 10 sit-ups a day, your love handles will miraculously disappear? Well, think again. Fitness experts say it's impossible to spot-reduce fat without toning and trimming your entire body. In fact the love handles will probably be the last thing to go, because that's where most of your fat is stored.