Okay, I'm curious, why does a lower intensity workout supposedly help burn fat? My primary goal is weight loss, I'm not training for a marathon or anything... but don't you burn more calories at a higher intensity and heart-rate? Wouldn't that aid a bit more in my weight-loss efforts?
At the gym I normally get my heart rate right up in the high intensity and work up a good sweat, but I kept my heart rate at 130 (my supposed fat burning zone...) for 30 minutes, but I didn't feel like I'd really driven myself or done much good.
I've tried looking it up online, but every website seems to say something different. Some say that the "fat burn zone" is a complete myth and that it's not the optimum way to lose weight, and others say that the pounds will come off a lot faster if you do low intensity workouts.
The theory is like this: There are two kinds of energy-burning processes, one is "aerobic" and one is "anaerobic." The first one is what happens when there is plenty of oxygen; the second is what happens when someone is really pushing hard and can't breathe fast enough to catch up to the body's need for oxygen.
"Aerobic" activity burns fat more efficiently than "anaerobic" activity. This is because of the biochemistry of how the body uses foods for fuel.
One way to tell if you are exercising in the "aerobic" range is to use your heart rate. It should be something like 60 percent of your max heart rate when you're exercising to stay "aerobic." Max heart rate depends on age.
If you exercise so vigorously that your heart is just pounding like mad and you can't catch your breath, you've gone over into the "anaerobic" process, and you'll burn less fat.
That said, some people like to do interval training, where you go along in the aerobic range for so many minutes, and then push for so many minutes (usually not as many!) to try to build stamina.
Many, many people OVERexercise, thinking that more must be better. For losing weight, it is not necessary to go to an extreme.
I'd like to point out, though, that this refers to what you are burning DURING THE EXERCISE. So, for example, during aerobic exercise, you're burning from your fat stores, which is why they refer to this as "fat burning" exercise. But if you start working anaerobically, you start burning from other energy sources in your body - your glycogen stores, blood glucose, etc - and all of THOSE things will have to be replenished after your workout. Much of the calories to do so (though not the actual carbohydrates) will come from your fat stores anyway, resulting in a net loss of fat regardless of what type of exercise you do.
MYTH with a grain of FACT. Lower intensity= higher fat burning is largely a myth. The aerobic range is pretty large. If you can sustain the effort for a long period of time, it is aerobic, anaerobic can only be sustained for short intervals
FACT: The lower your heartrate the higher the PERCENTAGE of calories burned that will be directly from fat stores.
This fact has led people to say that you should keep your workout at lower heartrates. BUT the highest percentage of fat burning is at rest...so would you say lay on the couch all day? NO
What matters is TOTAL CALORIES BURNED, and for that higher intensity burns more...plain and simple. While you are working out more of the burn will be stored carbohydrates (glycogen) BUT when you are done working out and are resting again, the body will store ingested carbs back in the muscles and burn FAT to provide energy.
You should be working at a level that you can maintain for at least 20 minutes, but it should be WORKING. Within that 20 minutes you can do short bursts higher --even into the anaerobic zone.
What matters in exercise is the total number of calories burned, not the source of fuel. The so-called "fat burning zone" is a myth, perpetuated by cardio machine manufacturers. My personal trainer textbook devoted an entire subsection of the cardio chapter to debunking the myth, yet it's still out there.
Sure, you may burn a higher percentage of calories from fat at a lower intensity, but your overall calories are so much lower that the fat calories burned are small.
At a higher intensity of exercise, you're burning so many more calories that it doesn't matter what % is from where. After all, weight loss is a matter of creating a calorie deficit, and the more calories you burn from exercise, the more you're adding to your deficit.
Did you know that you burn almost 100% fat when you're lying in bed? But how good of a workout is that? Edited to add: Ennay and I were posting at the same time and we used the same example.
Generally speaking, exercise at 65 - 75% of your max heart rate is considered low-intensity (the mythical "fat burning zone"), 75 - 85% is moderate intensity, and 85 - 90% is high intensity. When you get over that 85 - 90% threshold is when you shift from the aerobic to anaerobic zones that Jay is talking about.
I agree with Jay that interval training is the best way to maximize fat loss. Studies have shown that moderate intensity cardio interspersed with high intensity sprints into the anaerobic zone creates a large EPOC - that is, Excess Post-exercise Oxygen Consumption. Which, in English, means that you're metabolism is elevated for hours after you exercise and you burn calories at a much higher rate for up to 24 hours afterwards.
I like to keep my heart rate around 85% for two minutes and sprint up to 95% for a minute, drop back to 85% for two minutes, repeat, repeat for my cardio sessions.
'Scuse me, but I don't think I ever said that lying in bed was aerobic exercise...
BTW, I used to watch women at Curves going gangbusters on the machines and hopping up and down on the rest stations because doggone it, they could NOT get their heart rate up to the 100% level where it should be! It was only at 90%! And it's a wonder they didn't keel right over!
'Scuse me, but I don't think I ever said that lying in bed was aerobic exercise...
BTW, I used to watch women at Curves going gangbusters on the machines and hopping up and down on the rest stations because doggone it, they could NOT get their heart rate up to the 100% level where it should be! It was only at 90%! And it's a wonder they didn't keel right over!
Jay
LOL And here after going to Curves for awhile, I was hopping up and down on the rest stations, doing lunges, jumping jacks, whatever, just to try and get my heartrate to the 60% range! It seemed the more I worked out, the harder it became for me to get my heart rate up. I even took an advanced session, where you go around the circuit once, then increase your reps by 3 each, to see if I could get in more of an aerobic range, toward 70%. I could seldom reach it. I could get it up there on the resting station, but I'd put everything I had into the equipment and anytime we did a heart rate check on the equipment, my rate had dropped again. Like the equipment just didn't work me hard enough...even though I outdid anyone else's reps and felt like my limbs were going to fall off.
I bet it would have been pretty high. Snow shoveling is intense exercise, which is why so many out-of-shape guys keel over when they try it. I always call it snow-shoveling cardio (or leaf cardio, depending on the season).
At the point where I couldn't get my heart rate up high enough, I left Curves and joined a regular gym, where I could change resistance without having to go faster. My resting heart rate is around 56.
Terrific topic and great answers! I have had these same questions.
I work out for an hour, 6 days a week, using the elliptical and the treadmill. On the elliptical I usually do three miles and burn around 600 calories. It's great to see such a big number of calories burned. I just wish the dang machine didn't hurt the bottom of my left foot so bad or I would do an hour on it and skip the treadmill. Although, I do wonder if the treadmill is working my body differently and that is good for my toning as I lose the weight?
I would also love to hear what the opinion is on the weight machines. Should I be going heavy and slow with the weights, or light and fast? I am really confused on how to use those weight machines to my full advantage.
Fact or Fiction? Help!
Edited to add: Ennay and I were posting at the same time and we used the same example. 
It was only at 90%! 
