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<p>That’s what all the labels on treadmills would have you believe. The logic is that you are burning a higher percentage of the calories being burned from fat. The problem is that you aren’t burning very many calories. When you crank the intensity way up, the energy comes more from burning stored carbohydrates (glycogen) and less so from fat (as a percentage), but you are burning a ton more calories and more total fat.</p>
<p>However, I don’t even think that’s the issue because, frankly, the calories you burn from exercise (over and above the large number you are already burning just sitting on the couch) are not significant in the grand scheme of things. Instead, there appear to be benefits of exercise on your hormonal balance (Insulin resistance, growth hormone, testosterone, etc.) and those hormonal issues determine whether it’s easy or hard to lose stored body fat, not just while you are exercising, but for as much as 24 hours afterwards. For example, if you become more sensitive to insulin, you will tend to store less fat period, 24/7, 365 days a year than someone is more insulin resistant. The impact of exercise on hormones may explain why exercise hasn’t been shown to have much impact on weight loss in studies, but has been shown to be absolutely critical in keeping the weight off. Basically, we have no prayer of keeping weight off without exercise.</p>
<p>From a fat loss standpoint, the best advice I’ve seen is to focus on exercise that:</p>
<p>a) builds lean muscle (resistance strength training)
b) cranks up your metabolism (short bursts of high intensity/high heart rate exercise rather than long hours of low intensity exercise).</p>
<p>There’s room for all of it. You can only do resistance strength training two or three days a week. You really need a day off in between workouts. And, high intensity cardio intervals (90% to 100% of your max heart rate) are just so miserable that you can only do them a couple times a week, tops. So, there’s a place for a nice walk or some other fairly low heart rate exercise.</p>
<p>If you want to do any kind of endurance distance stuff: running, or long distance swimming, or bike riding, then you have to do long sessions of low intensity/low heart rate training in order to develop that kind of stamina/fitness. But, it’s not the most effective way to lose body fat. It’s actually training your body to burn less energy per minute. For losing body fat, you want to be inefficient – burning more energy.</p>
<p>As a practical matter, if you can do some kind of exercise that gets you bent over panting like a dog, sweating bullets for a few minutes, a couple of times a week, you’ll be ahead of the game for fat loss. High intensity is good, but it has to be in small doses.</p>