Straight, No Chaser: Fat Burn vs. Cardio – How Do I Best Exercise?

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You’re working out. Congratulations! But do you know what you’re doing?

If you’ve ever been to a gym, perhaps on an elliptical, a treadmill or stationary bike, perhaps you’ve seen a table like this. (You may want to click the pictures and tables to enlarge them.)


Your target heart rate zone points to a range of health and fitness benefits based on how much energy you exert during your workout. With that in mind, let’s discuss two of the settings you’re likely to see on your exercise equipment: fat burn and cardio.


It’s best to view your workouts as achieving incremental benefits. Any physical activity burns calories. Calories are units of energy, and you burn energy to lose weight. If you burn enough calories (relatively to how many you take in), you will lose weight. (We’ve discussed that previously here.)
Now your body has different ways of storing energy. Depending on how intensely you exercise, you will preferentially attack different energy stores. The important point is that different levels of activity and exercise progressively take you from burning calories to burning fat to improving your heart’s conditioning.

  • Fat burn: A lot of the confusion among those starting to exercise is found in the seemingly intuitive notion that people exercise because they want to “lose fat” rather than also thinking about “burning carbs” or “conditioning the heart.” In the hierarchy of expending energy, the body actually burns a higher percentage of fat relative to carbohydrates at lower levels of exertion. Lighter workouts afford the body a greater level of oxygen, which is needed to burn fat most efficiently. This level of exercise corresponds to reaching approximately 65% of your average maximum heart rate.
  • Cardio: When your exercise level reaches approximately 80-85% of your maximum heart rate, you’re in cardio mode, which means you’re working at a level sufficient to strengthen your heart and cardiovascular system. This level of exercise also best improves your blood pressure and lowers your cholesterol levels. In the grand scheme of things, cardiovascular fitness is much more important than fat burning. It’s important to note that at the higher levels of exercise, you don’t lose any of the benefits obtained at the lower levels of exercise.


So let’s clear any confusion regarding fat burning, weight loss and exercise. When you exercise in cardio mode, you exhaust your oxygen stores to the point where you aren’t as efficient in burning fat, although you are still doing so. In cardio mode, you switch to preferentially burning carbohydrates, which doesn’t require the same oxygen levels as fat to be utilized for energy. This point is illustrated in the following table.
If weight loss is your goal, you will absolutely burn more calories (and more fat) in cardio mode than fat burning mode. Fat burning mode points to the intensity level needed to start the fat burning process. For the most comprehensive workout, incrementally increase your workouts until you can perform in the cardio mode, because what you care about is the total number of calories, not the percentage of fat burned. And yes, you’ll still look better burning more calories than focuses on burning a higher percentage of fat relative to carbs.
Finally, as a measure of health, know your target resting heart rate. Where you fall in that range is a decent measure of your level of fitness.


Don’t forget to consult your physician before you begin an exercise routine. Feel free to contact your SMA expert consultant with any questions you have on this topic.
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12 thoughts on “Straight, No Chaser: Fat Burn vs. Cardio – How Do I Best Exercise?

  1. Nice! I was so glad to see you showed that one doesn’t burn less fat at a higher intensity; it just adjusts the ratio. That’s a common myth that more need to be educated on.
    However, I’m curious why you lean toward age-predicted HR versus RPE. Considering the high variability in age-predicted max HR, many will end up being way out of range. Unless they do max-testing, it’s just a best guess at their HRmax. RPE or other subjective intensity scales allow for individual variation.
    What are your thoughts?

    1. Hi, ExerCYser. First of all, you’ve absolutely correct. The answer to the question is something I am commonly guilty of on Straight, No Chaser (just ask any of my physician colleagues!). In the effort to present digestible information to the lay public, I often choose to present (err toward) the simplest version of information, often leaving out nuance that is present when I lecture or present in an academic setting. Regarding today, I offer my apologies to those more advanced in the exercise game, but as a public health initiative (which Straight, No Chaser is), that level of specificity is beyond what my average reader will retain or use when starting an exercise routine. My goal is always to get people stimulated enough to get started and working with professionals who will then provide the appropriate level of nuance. Thanks for your comments and following Straight, No Chaser!

      1. Thanks for your prompt response, Jeffrey.
        I do see your point. Once the calculations are performed, it’s quite easy to use the estimated HRmax. However, if a beginner is using it, I highly encourage them to begin at a low %. Then, they can then gauge the intensity (feels like) to compare with the estimated % they’re at (I.e., feels like 30%, but the estimate says 50%).

    1. Hi, Lee. Ok, let’s get in the weeds a bit (this is what the comments section should be for!). RPE is an acronym for rate of perceived exertion and is used for slightly different purposes in the training world and the medical world. In sports and training, the various RPE scales may demonstrate fitness through that perceived level of exertion. The better tuned athlete will perform similar activity with a lower perceived level of exertion than a less well tuned exerciser. This level of intensity and effect really speaks to your level of cardiovascular fitness.

    2. In your physician’s office (e.g. during a cardiac stress test), the perceived level of exert is an important consideration at the lower levels of function. Patients with a lower ejection fraction (i.e. a measure of the ability of the heart to sufficiently push enough blood around the body with each contraction) will have a higher rate of perceived exertion at lower levels of activity. Physicians may coordinate with trainers at the beginning of a program to set parameters of training based on this (this is why you “consult your doctor before starting a treatment program”). There’s more to it that this, but that’s a good start. Thanks for your question and for following Straight, No Chaser.

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