Does low-intensity, long-duration exercise really "burn fat" at rates higher than highly aerobic exercise? Is the academic case for this view actually strong? It seems like a lot of accepted knowledge in the exercise industry has a weak scientific basis.

2 Answers 2


From the American Council on Exercise:

In a 30-minute aerobic exercise:

Low Intensity (50% of maximum exercise capacity):
- you'll burn approx. 200 calories, 120 of them from Fat (60%)

High Intensity (75% of maximum exercise capacity):
- you'll burn approx. 400 calories, 140 of them from Fat (35%)


while it is true that a higher proportion of calories burned during low-intensity exercise come from fat (about 60 percent as opposed to approximately 35 percent from high-intensity programs), high-intensity exercise still burns more calories from fat in the final analysis.

Dummies.com concurs:

... working at a lower intensity requires less quick energy and a higher percentage of fat is burned. But you'll also burn fewer calories than you would if, for the same amount of time, you work out at a harder intensity (e.g. running versus walking).

During the same amount of time you don't use more calories at lower exercise intensities.

If you're trying to lose weight and you have only 30 minutes to work out, you would burn fewer calories walking at a moderate pace compared to walking at a fast pace.

The conclusion is:

Working out at higher intensities may cause you to burn a lower percentage of fat, but since you burn more total calories, you still use more fat calories.

  • More sources on this: scienceblogs.com/obesitypanacea/2010/06/…
    – Lagerbaer
    Commented Apr 21, 2011 at 14:55
  • Does that mean the extra calories burned from high-intensity are from muscle?
    – KallDrexx
    Commented Apr 21, 2011 at 17:27
  • 1
    So, if one is fat, wants to lose it, does not have a lot of $ to buy extra food, and has all the time in the world (e.g. a homeless person), then they should just walk around all day instead of running for a couple of hours.
    – Job
    Commented Apr 21, 2011 at 17:53
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    don't forget that the low intensity workout can be maintained for longer than the high intensity workout, especially by untrained people. So someone's who's not in a great physical shape might be able to do the 30 minute low intensity workout, but no more than 10 minutes of the high intensity workout. He's thus better off doing the low intensity workout as his benefit per session is improved. The conclusion from dummies.com is of course false. "you burn less fat, but because you burn more you burn more fat anyway" is logically wrong. The rest which gets burned is protein and carbohydrates.
    – jwenting
    Commented Apr 22, 2011 at 7:41
  • @jwenting - you are right, for someone who is not very fit a long low-intensity workout could be more beneficial than a short high-intensity one. The 'Dummies' conclusion is for a 30-minutes workout, even though the 'fat percentage' is lower, the 'total' amount ends up being higher. (But, in a short workout the low-intensity would indeed burn more fat)
    – Oliver_C
    Commented Apr 22, 2011 at 10:14

Looks like you are right and the fat burning zone is a bit of a falicy. To quote this research:

enter image description here

And they also have this table to show the results:

enter image description here

At 9 times the fat burning power of low intensity exercise I know what i'm going to be doing to lose weight!

** Edit **

I guess I need to clarify this. The study above is trying to debunk some of the conventional wisdom about the fat burning potential of exercise regimes. Two regimes were run, a low intensity study programme (ET) and a high intensity study programme (HIIT).

To add another table from the link study:

enter image description here

looking at the bottom row of the table, you can see that the ET group lost (ignoring the +/- to make the math easier) 4.5 subcutaneous skinfolds, whereas the HIIT group lost 13.9 subcutaneous skinfolds.

The ET programme resulted in more total time working out and used 120.4 +/- 31.0 MJ of energy. The HIIT programme resulted in less total time working out and used 57.9 +/- 14.4 MJ of energy.

Or from a percentage point of view the HIIT group did roughly 48% (57.9/120.4 for the percentage) of the work that the ET group did, but the people on the HIIT study lost more body fat (note that average overall weight loss was virtually non-existant for both groups).

If you now take that 48% and extrapolate it up to 100% it works out at an equivalent subcutaneous skinfolds loss of 28.99 (13.9/0.48), this equates to about 6.5 times as much subcutaneous skinfold loss. Now i'm not a mathmatician, and I have only taken one row on the table into account without taking any standard deviations into account the the above workings out are going to be messy and inaccurate, but they should hopefully illustrate the point.

High impact workouts are better at reducing body fat than low impact workouts and the point of this study was to debunk the conventional wisdom given by health professionals.

  • 1
    me too: I am going to sit on a couch watching TV with sandbags in my lap and throw one on the floor occasionally.
    – horatio
    Commented Apr 21, 2011 at 14:08
  • Note: It says relative to the energy costs!
    – Lagerbaer
    Commented Apr 21, 2011 at 14:29
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    This is a perfect example of how studies are not read carefully, and then some extraordinary claims are based upon this. The relative fraction of energy from fat is higher in the fat burning zone, but the total number of calories burnt is much lower. See the other answer on this.
    – Lagerbaer
    Commented Apr 21, 2011 at 14:55
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    I think I misread your answer. Especially your final sentence had me fooled. I'll remove my downvote asap.
    – Lagerbaer
    Commented Apr 21, 2011 at 17:51
  • hmm what did you think I meant? Seems like a got a lot of flack for this one.
    – Ardesco
    Commented Apr 21, 2011 at 22:08

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