Exercise: Is there any difference between "fat burn" and "cardio" workouts?

I got a new heart monitor for my workouts (usu. 30 min on a stationary bike, 40% of the time spent at high torque/high intensity). It tried to sell me on a distinction between “fat burning” and “cardio strengthening” modes, without fully explaining what the distinction between them was, exactly.

I mean, the more work and effort you put into it, the more calories you burn off AND the more you exercise your heart muscle, right? Or is a steady pace, 130 BPM, what they mean by “fat burning”, while if I pump up the effort and the torque knob, alternate going up over 160 and resting as it drops to 145 or so, that is what a cardio workout is.

Or is it just hollow talk, a distinction that actually doesn’t exist?

I think the “fat burning” and “cardio zone” things are outdated myths. Most of the current evidence suggests that for both fat burning and cardiovascular benefit you should be doing high-intensity interval training, not steady slow endurance work.

You got a cite for your “most of the current evidence suggests…”? Steady slow endurance exercise will increase your fitness, strengthen your heart, and burn fat, but of course would take longer. In fact slow jogging will burn more fat than speed work because in speed work your body cannot use fat but must rely purely on sugar. Fat requires more oxygen to be useful for exercise.

Certainly there’s a difference. But what it is, is not really completely known, and what the absolutely best kind of exercise routine is, is also not really known. Opinions and theories are everywhere.

Bear in mind the point of exercise is what happens during recovery. It’s how your body reacts after the exercise is all over that is what you want to control. What you want is an adaptation: you want your body to respond to the stress by changing its biochemistry, so that, first, the next bout of exercise is easier (you get stronger), and often, second, so that your body is better able to cope with its baseline stresses (you live longer). It is certainly not just a question of “the more physical stress the better,” in terms of provoking the desired biochemical changes. There are certain patterns of physical stress that are likely to provoke the fastest and most optimum shift in biochemistry during recovery. Unfortunately, we don’t know what they are, since it’s an incredibly complicated subject. Furthermore, they probably vary with age, sex, diet, history, current level of fitness, genetic dispositions, current risk factors, time of day, time of cycle (for women), relationship to other stressors, et cetera and so forth. That is,they’re probably highly individual.

Probably the best you can do is read all the hypothesis and theories, discount all that have too obvious an axe to grind or obviously don’t apply to you, and then experiment to find out what works best for you. For what it’s worth, my impression is that the only useful general advice is that an exercise “diet” should be varied just like your actual diet should vary (meaning you eat a variety of foods). It should probably include some long slow endurance work, some intense short cardiac max output work, some strength work, some flexibility, balance and coordination work, and so on. This has the additional virtue of being less boring.

What about those who exercise simply to burn calories? The point of such exercise has nothing to do with recovery, it’s about the energy expended during the exercising itself.

Not true. There’s an effect called afterburn, where if someone exercises hard enough, their metabolism is raised and they burn extra calories after the workout is done. But you have to exercise quite hard to get this effect. The “fat burn” level of working out isn’t hard enough.


Not true, exactly. An increased metabolism for a period post-work out only applies to certain types of exercise. Those who run to burn calories do not experience much metabolic after burn. Those who lift weights, on the other hand, have metabolically active systems for hours after the workout itself.

Now, the overall calorie burn of weight lifting is still less than that of pure cardio. This is because the relatively modest calorie burn of a weight lifting workout is only aided by the fairly small increase in calorie burn from metabolically active muscles. Cardio quickly burns calories and it’s not long before you’ve burned several hundred calories. So that alone is a greater calorie burn than the combination calorie burn of anaerobic weight lifting.

Double post

The study I cited (OK, I cited a NY Times article, but it cited the actual study) had the subjects engaged in cardio. They were riding stationary cycles, but I expect any cardio exercise would work the same. The thing is, you have to exercise a lot to get the effect, much more than I see almost anyone do at the club I belong to.

BTW, I do put in 45 minutes on a stationary cycle working out quite hard. And yes, it does help me lose weight. I only do this when the weather’s bad; otherwise I go cycling for a couple-three hours with steep hills. That helps me keep the pounds off, too.

I don’t know anything about afterburn for weightlifting. I didn’t even know it was a thing.

Second the call for a cite on this, but I think at the least you’d have to amend this to “…for faster results”, because of course endurance work is going to burn calories; you body doesn’t get to defy the laws of physics.

Yes, and I think this touches on what is probably the answer to the OP.
If fat-burning is paramount then it’s better to start at a relatively comfortable speed for 20-30 minutes, purely as a warm-up and to get the body to start burning fat. After that you can run whatever speed you like – the important thing is just not to get tired out in the warm up phase and then have difficulty running when you’re body is in the “useful” phase of burning fat.

If we don’t care about proportion of fat or sugar burned then the whole workout could potentially be less than 30 minutes, if that’s what you prefer, as it’s (almost) a linear equation of intensity * time.

Oh, and I should also say that even if you’re only doing short workouts your body will ultimately burn fat. It can convert fat to glucose if necessary. It’s just not happening so much during the workout, so that style of workout is not optimal for that purpose.


Your body can’t convert fatty acids into glucose.

The “you don’t burn fat if you exercise too hard” thing brought up earlier is also incorrect. You basically burn the same amount of fat when you exercise moderately or hard. It’s just that when you exercise hard you also burn a lot of glucose. So as a fraction of the energy used, the amount of fat burned goes down, but the absolute amount stays the same.

And remember that glucose stores are limited. Once you burn through your glycogen stores it’s fat all the way.

But it doesn’t really matter. Suppose you only burn glucose during your workout. Now you don’t have any left the rest of the day so you use up more fat. Result: same amount of fat gets burned.

The most important thing is whether you can keep yourself from eating extra after your workout.

Firstly I didn’t say fatty acids. But secondly even this seems misleading as your body can convert fatty acids to triglycerides and triglycerides to glucose (cite1, cite2)

A triglyceride (aka fat) is a molecule made of three big fatty acids and a small glycerol backbone. When you break up the triglyceride you can use the glycerol to make glucose, but not very much as the glycerol is only such a small part of the triglyceride.

Unless I’m very much mistaken you can’t get glycerol from fatty acids and you can’t get triglycerides from fatty acids without adding glycerol.

If your body can’t convert fat to glucose, then what does it do with it? Is there some way to convert fat directly to ATP without using glucose as an intermediate?

There is.

Some high intensity interval training is superior cites. There are a lot, here is a quick random sample:

People who simply perform steady endurance work generally don’t lose much if any weight, and those that do usually stop losing weight after the first few weeks. That’s because your body quickly adapts to it and then you burn very few calories per mile and don’t have any “recovery” period afterwards to burn even more calories.

“Exercisers in a 2009 study conducted by researchers at Queensland University of Technology in Australia who did steady-state cardio five times a week for 12 weeks lost only 7 pounds on average — and nearly half of them lost less than 2 pounds.”

If you do high intensity interval training, you rapidly deplete your glycogen stores and have to quickly switch to burning fat for the rest of the workout. The workout is also intense enough to encourage your body to build more muscle-and growing more muscle is the key to weight loss. Muscle is greedy for calories. Low-intensity aerobics do not build muscle.

The primary reason why people get fat as they get older is because after age 30 your muscles start to go away. So you simply don’t need as many calories per minute to exist, and if you keep eating the same number of calories as when you were 20, you’ll put on body fat.

If your primary exercise goal is to lose weight, go for heavy-duty weight-lifting and skip all other forms of exercise.

Ah ok. (My) ignorance fought.

Those studies appear to be targeted at specific medical situations (e.g. prediabetes) and not for weight loss. I’m a bit dubious that one’s body can learn to burn very few calories when exercising. It’s still a physics problem: moving a mass one mile takes up a certain amount of energy no matter what the body has learned.

I can believe that high endurance exercise is better for weight loss but if so my guess is that it’s unrelated to how efficiently the body burns the calories; e.g. people might stick to HE exercise longer than steady endurance.

In the end, though, I think it’s largely irrelevant. Cutting back on caloric intake is much more important for losing weight than exercise.