From Clarence Bass' Website...
What About Fat Loss?
Angelo Tremblay, Ph.D., and his colleagues at the Physical Activities Sciences Laboratory, Laval University, Quebec, Canada, challenged the common belief among health professionals that low-intensity, long-duration exercise is the best program for fat loss. They compared the impact of moderate-intensity aerobic exercise and high-intensity aerobics on fat loss. (Metabolism (1994) Volume 43, pp.814-818)
The Canadian scientists divided 27 inactive, healthy, non-obese adults (13 men, 14 women, 18 to 32 years old) into two groups. They subjected one group to a 20-week endurance training (ET) program of uninterrupted cycling 4 or 5 times a week for 30 to 45 minutes; the intensity level began at 60% of heart rate reserve and progressed to 85%. (For a 30-year-old, this would mean starting at a heart rate of about 136 and progressing to roughly 170 bpm, which is more intense than usually prescribed for weight or fat loss.)
The other group did a 15-week program including mainly high-intensity-interval training (HIIT). Much like the ET group, they began with 30-minute sessions of continuous exercise at 70% of maximum heart rate reserve (remember, they were not accustomed to exercise), but soon progressed to 10 to 15 bouts of short (15 seconds progressing to 30 seconds) or 4 to 5 long (60 seconds progressing to 90 seconds) intervals separated by recovery periods allowing heart rate to return to 120-130 beats per minute. The intensity of the short intervals was initially fixed at 60% of the maximal work output in 10 seconds, and that of the long bouts corresponded to 70% of the individual maximum work output in 90 seconds. Intensity on both was increased 5% every three weeks.
As you might expect, the total energy cost of the ET program was substantially greater than the HIIT program. The researchers calculated that the ET group burned more than twice as many calories while exercising than the HIIT program. But (surprise, surprise) skinfold measurements showed that the HIIT group lost more subcutaneous fat. "Moreover," reported the researchers, "when the difference in the total energy cost of the program was taken into account..., the subcutaneous fat loss was ninefold greater in the HIIT program than in the ET program." In short, the HIIT group got 9 times more fat-loss benefit for every calorie burned exercising.
How can that be?
Dr. Tremblay's group took muscle biopsies and measured muscle enzyme activity to determine why high-intensity exercise produced so much more fat loss. I'll spare you the details (they are technical and hard to decipher), but this is their bottom line: "[Metabolic adaptations resulting from HIIT] may lead to a better lipid utilization in the postexercise state and thus contribute to a greater energy and lipid deficit." In other words, compared to moderate-intensity endurance exercise, high- intensity intermittent exercise causes more calories and fat to be burned following the workout. Citing animal studies, they also said it may be that appetite is suppressed more following intense intervals. (Neither group was placed on a diet.)
The next time someone pipes up about the fat-burn zone, ask them if they are familiar with the Tabata and Tremblay research reports.
[You'll find high-intensity aerobic workouts for bodybuilding in Ripped 3 and for balanced fitness, strength and endurance, in Lean For Life; both books are in the products section of this site. Routines specifically applying Tabata-type intervals are explained in chapter 5 of Challenge Yourself. Keep in mind that VO2max can only be measured in the laboratory; you'll have to estimate 170% of VO2 max. Don't try to make it too complicated. Simply chose a pace that brings you near exhaustion on the final 20-second rep; you should become more fatigued with each rep. Increase the pace as your condition improves. It's always better to underestimate your ability at the start. Begin a little slower than you think you can handle, and then adjust the pace from workout to workout. Don't attempt high-intensity intervals unless you are in good condition; they're not appropriate for beginners. Note the medical warning which follows.]
Warning
The Tremblay group and Dr. Tabata, in his e-mail response to Richard Winett, emphasize this warning: "High-intensity exercise cannot be prescribed for individuals at risk for health problems or for obese people who are not used to exercise."
The only caveat I can think of is that it depends on your carb intake. If you're doing a Jay Cutler type diet and are dieting on (relatively) high carbs, then this will probably work. However if you're on the low end (.5 g per lb), then this could be risky in you lose muscle easily.
I think of it like this: you do weights, then you do HIIT cardio. You've probably devastated glycogen stores. Therefore the body will have to use the fat stores as fuel for energy. It should also store glycogen preferentially.
The slow state cardio will spare your glycogen stores, but less fat will be burned overall as we all know that the body's preferred fuel is carbohydrate. So if it still has carbs that it can use, it will use those instead of the fat stores.
So steady state cardio will burn mostly fat during it, but little to no fat afterwards. HIIT cardio will eat into glycogen tremendously, but fat utilization will be high afterwards. Just the way I think, no proof or anything. I tend to hold onto muscle (slow metabolism), so I use HIIT with no problems. Guys who tend to burn muscle off should probably stick to steady state.
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