Time is a commodity. You have only so many hours in the day to get your obligations met, so you need to be efficient and effective with everything you do – exercise regimen included. Besides, who wants to carve time out of their busy schedule to do a workout that doesn’t give them the results they want? Well, as long as you know the basics, you won’t have to worry about that.When it comes to fitness, most health experts would like you to believe that you won’t get much benefit unless you do at least an hour a day. While that is great in theory because it would definitely be wonderful for your health, not many people have that kind of time to devote to their fitness program. And, if you do, you don’t always want to fill it with “must do” activities as you would like to have a little fun in life too.So, how long do you need to exercise before your body starts to burn fat like a hot stove with a dry piece of wood? According to Penn State University, the answer is 12 minutes.Now, this doesn’t mean that you can engage in a 12 minute exercise session and declare yourself physically fit. This length of time does not include a warm-up or cool down and the 12 minute mark is when your body begins to release the enzymes that burn fat. Therefore, everything you do after that length of time activity-wise will help your body use your excess fat for fuel.The key is to be in your target heart zone. This is when your heart rate is 65-80% of your maximum heart rate. To calculate this number, take 220 minus your age, and then figure out what 65% and 80% are. For instance, if you are 40 years old, your target heart zone is 117-144 beats per minute (220-40 = 180, 180 x .65 = 117, 180 x .80 = 144).You can make sure you’re in this fat burning zone by taking your pulse at random intervals or by wearing a monitor. Either way, you’ll be burning calories ultra-fast when your heart rate is right where it needs to be – for more than 12 minutes, that is!