Am I Burning Fat Or Carbs When I Exercise?

The source of your body’s fuel is largely determined by the intensity of your exercise.  Many people are not performing their cardiovascular exercise at the proper intensity, especially if their goal is weight loss.  There are a couple of key considerations in determining the proper intensity of cardio for yourself, one being the primary goal of your cardio, and the other being the proper determination of your target heart rate during exercise.

First let’s address the goal of your cardio.  Many people want to lose weight when they perform cardio and with that in mind, the higher your intensity, the more calories that you will burn.  Also, if your cardio is to optimize the health of your cardiovascular system, the higher intensities will also prove more beneficial.  If you are trying to attain weight loss, and have many hours to spend doing it, the lower intensity exercise will work.

At higher intensities (>75% of maximal heart rate), you will burn a combination of fat and carbohydrates and your overall calorie expenditure is much greater than at lower intensities.  At lower intensity (<65% of maximal heart rate), the overall percentage of fat burned compared to total caloric expenditure is higher but the overall calories burned are much lower.

To understand this better, think of a hybrid car that uses a combination of power from batteries and gasoline.  At a higher speed, the car uses much more gasoline (carbs) in addition to battery power (fat), and the overall miles driven is much greater.  At a lower speed, most of the power used is from the batteries (fat) but the total miles driven are far less.  If you want to lose weight, I feel you should be more concerned about the total miles driven (total calories burned), unless you have considerable time on your hands to exercise at a lower intensity.

Now we have to determine your proper heart rate.  Most charts posted on treadmills and walls of gyms use a formula that underestimates the proper intensity by a great deal.  This formula is 220, less your age, times your intensity percentage and looks like this:  220 – 42 (age) X 70% = 125.  In this example, your heart rate should be 125 beats per minute during exercise, which is entirely too low.

The more accurate formula to determine your target heart rate uses your resting heart rate to determine your target heart rate during exercise.  The average resting heart rate for an adult is 72 beats per minute (to find your resting heart rate, take your pulse for one minute before you get out of bed) and I will use that in the following example.  The more accurate formula is 220, less your age, less your resting heart rate, multiplied by your intensity percentage, plus your resting heart rate.  Here is what is looks like:  220 – 42 (age) – 72 (resting heart rate) X 70% + 72 (resting heart rate) = 146 beats per minute.  As you can see, the heart rate was underestimated by 20 beats per minute with the more commonly used formula.

To summarize, first use the proper formula to determine your target heart rate and then remember the more intense your cardio, the more calories you will burn.

CategoryFitness, Nutrition

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