“Fat burn is greater when exercise intensity is high.” Izumi Tabata

I believe in high-intensity aerobics. In Ripped 3, for bodybuilders, I recommended “a variety of relatively short and infrequent aerobic sessions interspersed with explosive muscular effort.” In Lean For Life, published six years later, I emphasized high-intensity aerobics even more; I reduced the frequency of aerobic sessions to two times a week (in Ripped 3 I recommended up to four) and substantially increased the intensity. But it wasn’t until recently, when my friend Richard Winett, Ph.D., publisher of Master Trainer, called my attention to new research findings, that I came to fully appreciate the superiority of high intensity aerobics compared to the usual prescription that heart rate be maintained between 60% and 80% of maximum.

As explained in the nearby FAQ (Low intensity aerobics?), high intensity aerobics burns the same amount of fat as low intensity, but the expenditure of calories is substantially greater; plus, intense aerobics produces a higher level of fitness. Importantly, the more fit you become, the more likely you are to use fat as fuel for any given activity. And now, research in Japan and in Canada shows that short, very intense aerobic sessions are amazingly effective for both fitness and fat loss.

Maximal oxygen uptake, or V02max, is generally regarded as the best single measure of aerobic fitness. As the rate of exercise increases, your body eventually reaches a limit for oxygen consumption. This limit is the peak of your aerobic capacity, or your V02max. As intensity increases beyond V02max, your body must shift to anaerobic (without oxygen) energy production. An oxygen debt begins to build at this point and blood lactate levels climb. In general terms, one’s ability to continue exercising in the face of rising oxygen deficit and lactate levels is called anaerobic capacity.

This is important because many high-intensity sports (including basketball, football, soccer and speed skating) require a high level of both aerobic and anaerobic fitness. Clearly, total fitness involves both high V02max and high anaerobic capacity. A training protocol that develops both would be a godsend.

Izumi Tabata and his colleagues at the National Institute of Fitness and Sports in Tokyo, Japan, compared the effects of moderate-intensity endurance and high-intensity intermittent training on V02max and anaerobic capacity. (Medicine and Science in Sports and Exercise (1996) 28, 1327-1330). Interestingly, the high-intensity protocol had been used by major members of the Japanese Speed Skating team for several years; it’s a real-world training plan. As you will see, however, the protocol is unique among aerobic training programs for its intensity and brevity.

Many studies have been done on the effect of training on V02max, but little information has been available about the effect on anaerobic capacity. That’s because until recently methods for measuring anaerobic capacity have been inadequate. This study used accumulated oxygen deficit to measure anaerobic energy release, and is one of the first to measure the effect of training on both aerobic and anaerobic capacity.

Notice that the duration of the moderate-intensity and the high-intensity protocols are drastically different: (excluding warm-ups) one hour compared to only about 4 minutes per training schedule

Tabata’s moderate-intensity protocol will sound familiar; it’s the same steady-state aerobic training done by many (perhaps most) fitness enthusiasts.

Here are the details (stay with me on this): In the moderate-intensity group, seven active young male physical education majors exercised on stationary bicycles 5 days per week for 6 weeks at 70% of V02max, 60 minutes each session. V02max was measured before and after the training and every week during the 6 week period. As each subject’s V02max improved, exercise intensity was increased to keep them pedaling at 70% of their actual V02max. Maximal accumulated oxygen deficit was also measured, before, at 4 weeks and after the training.

A second group followed a high-intensity interval program. Seven students, also young and physically active, exercised five days per week using a training program similar to the Japanese speed skaters. After a 10-minute warm-up, the subjects did seven to eight sets of 20 seconds at 170% of V02max, with a 10 second rest between each bout. Pedaling speed was 90-rpm and sets were terminated when rpms dropped below 85. When subjects could complete more than 9 sets, exercise intensity was increased by 11 watts. The training protocol was altered one day per week. On that day, the students exercised for 30 minutes at 70% of V02max before doing 4 sets of 20 second intervals at 170% of V02max. This latter session was not continued to exhaustion. Again, V02max and anaerobic capacity was determined before, during and after the training.

In some respects the results were no surprise, but in others they may be ground breaking. The moderate-intensity endurance training program produced a significant increase in V02max (about 10%), but had no effect on anaerobic capacity. The high-intensity intermittent protocol improved V02max by about 14%; anaerobic capacity increased by a whopping 28%.

Dr. Tabata and his colleagues believe this is the first study to demonstrate an increase in both aerobic and anaerobic power. What’s more, in an e-mail response to Dick Winett, Dr. Tabata said, “The fact is that the rate of increase in V02max [14% for the high-intensity protocol – in only 6 weeks] is one of the highest ever reported in exercise science.” (Note, the students participating in this study were members of varsity table tennis, baseball, basketball, soccer and swimming teams and already had relatively high aerobic capacities.)

The results, of course, confirm the well-known fact that the results of training are specific. The intensity in the first protocol (70% of V02max) did not stress anaerobic components (lactate production and oxygen debt) and, therefore, it was predictable that anaerobic capacity would be unchanged. On the other hand, the subjects in the high-intensity group exercised to exhaustion ,and peak blood lactate levels indicated that anaerobic metabolism was being taxed to the max. So, it was probably also no big surprise that anaerobic capacity increased quite significantly.

What probably was a surprise, however, is that a 4 minute training program of very-hard 20 second repeats, in the words of the researchers, “may be optimal with respect to improving both the aerobic and the anaerobic energy release systems.” That’s something to write home about!

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?