What matters is that you are achieving your results. If that's what's happening, then no reason to change.

As for myself, I do a combination of both types of training.

I say shoot for the calories. I usually try to burn at least 300. So if I am walking, it may take an hour or running a half an hour.

But actually usually what I do is walk the turns and run the straightaways, interval training.

All of the above refernces to cardio zones fail to take into consideration the one element where most of us differ from the norm of the population. We don't have a stockpile of carbs to burn, and many of us don't even have very many free carbs floating around as blood sugar.

This means that choosing your level of intensity based on whether or not you want to burn fat or carbs is sort of a moot point. If you are in ketosis you are going to burn fat period, regardless of intensity level. However at higher intensity levels there may be some tendancies for the body to cannabalise muscle tissue to provide energy as well. Best way to make sure that doesn't happen is to make sure that you have plenty of protein before and after the workout.

Fat actually is a fairly efficient energy source once our bodies are used to using it fulltime.

So concentrate on what else you want to achieve - are you looking to increase your cardiovascular fitness? If so then you will need to work at a higher level of intensity, or cycle through a few levels with interval training.

However, if you are just after fat loss - the harder and longer you go - the more calories you will burn. As long as you are in ketosis, the majority of them should come from fat, due to the total lack of carbs in your body in the first place.

I find it amusing that no one agrees on the best way, scientifically anyway, to maximise fat loss with cardio exercise. That blurb reprinted from Precor says lower intensity increases metabolism in the long run, the article lined by dina1957 says the higher intensity increases metabolism.

I can appreciate the the sentiment of wanting to know the best way, scientifically, to maximise workouts, but I'm with the guy that says just do what you enjoy most. I have tried over the years treadmill walking, recumbent biking, elliptical machines, walking outside, believing I had to go for long periods at lower intensities to do the "best" workout for fat loss. I hated it, always, it was boring and I never stuck with it. I took up running (jogging) last spring and I LOVE it! My boyfriend used to have to blast my butt to get me to go for a walk, and now I pester him to go for a run all the time. I run at a heart rate that is not low, more like moderate to high.

At this point, I don't care if I'm not maximising my workout. I'm working out regularly and loving it. And that's way better for me than working out haphazardly and hating every minute of it.

Val

In the past I have spent a lot of time jumping rope, Airdyning, jogging, etc. I have found no difference in weightloss during this time when compared to just doing resistance training. Three winters ago I lost quite a bit of weight while doing nothing but Nautiuls circuits three times a week and watching my carb intake.

In my experience the strength training aspect of weight loss is a bigger factor than the "cardio/fat burning" aspect.

Jon

I have found that if i want to stay in the fat burning zone i have to be moving at a snails pace, and i dont see how that is helpful to me at all. I use the elliptical a lot and can do 30 mins with a heart rate of about 170bpm-180bpm. I have often wondered if this was good for fatloss or not.

I think kbfunTH is right. Too many people are locked into the fat-burning-zone idea without understanding the logic behind it.

My understanding is you are burning a mix of fat and carbs all day long. While sleeping the heart rate is at its lowest and you are burning almost entirely fat. While rushing around during the day you have periods, like running to catch the bus, where you are burning almost entirely sugar. Anytime you are breathing hard, you're burning sugar.

The fat burning zone is where you are keeping your heart rate low enough that you are burning mostly fat. For a newbie, that could be 50% of max heart rate. For a highly trained endurance athlete, 90% of max heart rate could still be fat-burning.

So walking on a level treadmill is fat-burning. Walking three miles and hour it would take 15 hours to burn one pound of fat. If you are jogging 5 miles an hour you are still in the fat-burning zone so it would take about 9 hours to burn one pound of fat.

For that elite athlete, he's still burning fat at 90% of max heart rate so it would take an hour or two to burn one pound of fat.

To revitalize a sleeping subject, this is what I found recently:

To lose FAT, one should exercise moderately for a longer period of time, rather than push hard for a shorter time. For example, if someone burns 200 cal in 30 min (at the high end of their Target Heart Rate), they are burning 50% stored body fat and 50% carbs. (100 cal of stored body fat and 100 cal of stored carbs)

If they take 60 min to burn 200 cal, they will use 80% fat and 20% carb, so that burns 160 cal of body fat and 40 cal. of stored carbs.

What I read said:
Any exercise seems better when it burns higher amounts of calories, as calories really do count for weight loss, however it is the calories used from fat that makes the difference. Remember there are 3500 calories in 1 pound of fat, so it is much better to be burning higher levels of body fat during each exercise.

The bottom line is that one should stay closer to the mid-to-lower end of one's Target Heart Rate to burn more fat.

144.......127.........110
85%......75%........65%

The above is according to the chart on my elliptical machine, for age 50 (I am 51).

This is from a workout website:
Zone 3 (70 - 80% of MHR) - This zone is the most effective for overall cardiovascular fitness and is often called the "aerobic zone" or "target heart rate zone". This is the optimal zone to workout in to increase your cardio-respitory capacity or the bodies ability to transport oxygenated blood to the muscle cells and carbon dioxide away from the cells. After a while you will be able to cover more distance during workouts in less time. Your body will burn less glucose and more stored fat as fuel thereby working more efficiently. This zone is also effective for increasing overall muscle strength.

According to this, my THR is 119 - 136 (70-80%) (around 128 - like my goal weight! Easy to remember! And this rate is quite strenuous enough for me at this time.

I hope this helps, rather than adds to the confusion.

Low intensity sessions to burn off fat
Brian Mackenzie

There are two key variables that we need to know:

1. Fatmax - the exercise intensity at which the highest rate of fat oxidation occurs
2. Fatmax zone - the range of exercise intensities in which the fat oxidation rates remain within 10% of Fatmax

Researchers from Birmingham University's Human Performance Laboratory attempted to pinpoint the exercise intensities at which fat metabolism is maximised in a study of 18 male endurance cyclists with a training background of at least three years. Their work found that the Fatmax Zone is between 68% and 79% MHR

Alternative research has suggested that when you cycle, swim, row or run at a modest intensity of only 50% VO2max (about 69% MHR), fat provides about 50% of the calories you need to keep going for the first hour or so. If you keep going after that, fat becomes even more generous, providing around 70% of the total energy after two hours and 80% or more if your work duration exceeds three hours. If you increase the intensity then the Fat contribution decreases - at 75% VO2max fat provides 33% of the energy.

Be aware that all the tests done to determine fat burning percentages were done on people who eat lots of carbs. Their results are not what low-carbers can expect. Without the high-carb intake, your body will be burning a higher percentage of fat at every level.

I have found that I can exercise for longer at higher intensities than I could when I ate lots of carbs (and ate/drank carbs while exercising). Once your body has adjusted to low carbing, it becomes a fat-burning machine at all levels of exercise.

What you're missing here is that the body will start looking for glucose in the muscles (or worse yet consuming the muscles themselves) to burn instead of fat.

Please explain. Unless it is starving, the body will not use muscles for energy.

If the body starts needing to use something other than fat as a fuel source and there are no 'carbs' to fuel that extra need then the body starts digging around for an additonal fuel source...
That's why working out at a lower HR is better for losing fat - the body's need for NRG is slow enough that "about 50%" of it can be delivered from fat.

At a higher HR the immediate NRG need is greater and the body can't convert fat to NRG fast enough ("If you cycle along at 75% VO2max, fat would provide 33% of the required calories") thus it starts looking for additional fuel sources at a greater rate than a 'Fat Burning' HR.

If there isn't enough glycogen/quick fuel to meet the need, where does the body get it's 'quick fuel' from?

Ketones can be burned instead of glucose for many body energy requirements. Thjs along with the increased ability to use fat for enegy is why low-carbers can do endurance exercise and not need the steady intake of carbs that others do. For example:

and from R. Brown, C. Cox, A. Goulding, High-carbohydrate versus high-fat diets: effect on body composition in trained cyclists, Med Sci Sports Exerc 32(3): 690-694 (2000)

That accounts for the fat part of your NRG needs.

What about the carb/'fast fuel' part of your needs?