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.
