There is a popular myth that dictates a specific range for your heart rate in order to burn fat. Most cardio machines have a display that will give you a “fat-burning zone” so you can zap that fat.
But what happens if you venture outside of that zone?
Do you still burn fat ?
When you exercise, you use both fat and carbohydrates depending on the type of exercise you are performing. Very low intensity like walking, fat is the first choice of energy source. As the intensity of the exercise increases up to your lactate threshold (the line in the sand where you go from purely aerobic to anaerobic) fat becomes less of the preferred energy source and carbohydrates start being used. When exercising just below the lactate threshold, you are using mostly carbs. Once past the lactate threshold you are only using carbohydrates as fuel.
If you exercise for a long time (90 minutes to 2 hours), your glycogen (think carbs in the muscle) and glucose (blood sugar) becomes low. This metabolic state threatens your muscle survival since carbs are your muscles preferred fuel. When carbohydrates are not available the muscles are forced to use fat. There is a catch. In order to sustain your workout and be able to exercise for that time duration, you need to eat carbs. So don’t think if you eliminate carbs you’ll burn more fat because chances are you’ll burn nothing because you’ll be on the floor passed out 
So DO eat your carbs.
Because more fat is used at low intensity exercises, most people assume that low-intensity is best for burning (hence where the idea of the “fat-burning zone” came to exist). Even though fat is used predominately right below the lactate threshold, the rate of calorie expenditure and the total number of calories burned are much greater than when exercising at lower intensities, so the total amount of fat used is also greater.
Your heart rate range can vary. Depending on if you are on certain medications, more physically fit or deconditioned. I like to use the RPE (rate of perceived exertion) along with a visual cue of my clients. This RPE is a scale from 1-10 (one is really easy and 10 is excruciatingly hard). You will hear me ask this quite frequently during my sessions. This is a great gauge of how hard you are working.
The bottom line, if you want to burn that fat, what matters most is the number of calories you consume verses the number of calories you expend. To lose weight, it matters very little whether those burned calories are from fat or from carbohydrates.
Side Note:
To get the most out of your workouts and really stoke that fat burning furnace, try the following:
Go For It!
A great way to decrease your waistline is with high-intensity interval training. Go easy for a short duration then go hard for a short duration, keep alternating this and you have your intervals. Not only does interval training quickly improve you fitness; it is more effective because it burns more calories in the shortest amount of time. PLUS (mega bonus) you will continue to burn calories because you have increased your post-workout metabolic rate.
Nicole Simonin,
Fitness Professional, CPT, PTA, LWMC
Check out our SIU Boot Camps to see how interval training can annihilate your body fat!
SIU Articles are not intended to treat or prescribe a specific workout program. Each person is different and unique. To get a personalized workout program please contact Shape It Up at 609-501-0587. And as with any workout program, always consult your physician before beginning a fitness program.
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Starting the challenge, I had been exercising, basically doing the treadmill most days but had kind of reached a point where I was not seeing any changes so I felt adding weights to my program would help. Little did I realize that boot camp would include jumping jacks,push ups and assorted other tricks that Nicole could come up with…
