Today I would like to discuss what really constitutes “exercise.” I have had several discussions with people about exercise and what kinds of things they should be doing to stay healthy. When it comes to your cadiovascular health, the type of exercise you do is not as important as just getting your heart rate up. The American College of Sports Medicine recommends as exercise frequency of 3 to 5 days per week at a heart rate range of 60-80% of your heart rate reserve. So what exactly does that mean? Everybody has a maximum beats per minute that their heart can beat. This max number is different for everybody and it decreases as you get older. The only way to know your true maximal heart rate is to do some type of a stress test where you do some activity, usually running on a treadmill, until you reach your max. These tests can be expensive. IF you do not have any heart conditions and you are a generally healthy person, you can use the 220-age formula. This formula has some significant limitations but is widely used in the medical community to estimate max heart rate.
So, now that you can guesstimate your max heart rate, how do you determine you heart rate reserve? A commonly used method, and the one I prefer, is the Karvonen formula. I know, we are talking way too much math but hang with me. You need to take your resting heart rate. Once you have that number AND your max heart rate (220-age), subtract the two (i.e. HRmax–HRrest=X). This new number (X) is your heart rate reserve. To find 60%-80% of that just multiply X by .6 and .8. Once you have those two numbers, add both of them to your resting heart rate. These two new numbers represent the range within which you should be exercising.
If you are working closer to 60% (the lower end) a greater percentage of the total calories burned will be fat calories (~50%). If you are working closer to 80% of your heart rate reserve, a lower percentage of your total calories burned will come from fat calories (~30%). BUT if the workout time is equal, you will burn more total calories working at 80% HRR and therefore you will also burn more total fat calories.
With this being said, the overall goal for exercise is not always burning fat calories. You may just be trying to maintain a healthy lifestyle. Well, exercising in the 60-80% HRR range you will accomplish that too.