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“One of the biggest myths is: When you work at a high-intensity anaerobic level, such as during interval training, you shut down your fat-burning machinery.” Arthur Agatston, MD, The South Beach Diet Super Charged (Rodale, 2008)

Intervals For (almost) Everyone

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Fitness-Health-Rehab-Fat Loss

In Ripped 3, published in 1986, I recommended short "bursts of high-intensity muscular effort in every aerobic session." Citing exercise physiologists Mike Stone and Harold O’Bryant, I said intervals are the best way to get the fat-burning benefits of aerobic exercise without sacrificing hard-earned muscle tissue. Eleven  years later, in 1997, about a year after this website came online, health psychologist Richard Winett and I reported on groundbreaking research by Dr. Izumi Tabata in Tokyo and Dr. Angelo Tremblay in Canada showing that several short, very hard intervals “may be one of the best possible training protocols" for improving aerobic fitness and burning fat; see articles 10 (http://www.cbass.com/FATBURN.HTM) and 11 (http://www.cbass.com/SEARCHOF.HTM).

Turns out that was just the beginning. The news on interval training has only gotten better over the last 10 years. The latest research shows that sprint intervals improve blood flow to the muscles and the heart; and that intervals are even good for people with heart failure and metabolic syndrome. What’s more, we’ve recently learned that cardiologist Arthur Agatston, MD, author of the hugely successful South Beach Diet series, “introduces” interval training in his latest book, The South Beach Diet Super Charged (Rodale, 2008). Let’s talk about the new developments.

Intervals Improve Artery Function in Less Time

It’s a given that high-volume endurance training (ET) improves blood flow to the heart and muscles. The specific effects of high-intensity interval training, however, have remained largely unexplored—until now.

Researchers at McMaster University in Canada reported online in the American Journal of Physiology-RIC (April 23, 2008) that “low-volume sprint interval training” (SIT) produced results similar to ET, with less than half the training time.

They recruited 20 untrained healthy males and females, average age 23, and had them perform six weeks of SIT or ET. The interval group did four to six 30 second “all-out” stationary-bike sprints, with 4.5 minutes recovery, 3 days a week; the endurance group did 40-60 minutes of moderate-intensity cycling 5 days a week.

They found that both forms of training improved artery structure and flexibility, i.e. blood flow. Both intervals and endurance training improved blood flow in the legs, but not in the carotid arteries—perhaps because young, healthy subjects don’t have enough initial carotid stiffness to show significant improvement.  

Maureen MacDonald, an associate professor in the Department of Kinesiology, said in a press release that the study demonstrates that people who are pressed for time can still benefit from training, if they are willing to work hard for brief periods of time.

“More and more, professional organizations are recommending interval training during rehabilitation from diseases like chronic [lung] and…cardiovascular disease,” MacDonald added. “We wouldn’t be surprised to see more rehabilitation programs adopt this method of training since it is often better tolerated in diseased populations.” (I’ve long argued that brief, hard training is not only more challenging, it is also more interesting—and motivating—than long, slow volume training, which is boring.)

Let’s look at some remarkable results in rehab next.

Intensity Beats Volume—for Heart Failure Rehab

Norwegian researchers conducted a comparison study like the one discussed above, but with older patients diagnosed with chronic heart failure; they also measured a wider range of cardiovascular effects.

Twenty-seven patients averaging 75-years-of age were randomly assigned to either moderate-intensity continuous training or high-intensity interval training three times a week for 12 weeks; there was also a control group simply told to stay active.

Both exercise groups walked on an “uphill” treadmill. The interval group, after a 10 minutes warm-up, did four 4-minute work periods at 90-95% of measured peak heart rate, separated by 3 minutes of active recovery. The continuous training group walked at 70-75% of peak heart rate for 47 minutes. The regimens were designed to burn the same number of calories.

The results reported in the June 4, 2007, issue of the journal Circulation  were, to say the least, noteworthy—favoring intervals in virtually every respect. (As expected, there were no changes in the control group.)

Peak aerobic capacity (VO2max) increased more with intervals than with continuous training; the difference was a whopping + 46% versus + 14%. The improvement was coupled with a significant beneficial remodeling of the left ventricle (LV), the large chamber of the heart, but only in the interval group. LV ejection fraction, an index of heart function, increased 35% in the interval group; no improvement was seen in the continuous training group. In addition, pro-brain natriuretic peptide, a marker of the severity of heart failure, declined by 40%--again in the interval group only.

And there’s more. As in the last study, artery flexibility and blood flow improved, this time in the principle artery in the upper arm—with “greater improvement” shown by the interval group than the continuous training group.

Quality of life improved in both groups, but again “more markedly in the interval subjects, which suggests that more intensive physical training is more rewarding,” the researchers wrote in their report. “Informal comments from the patients” indicated that the interval group enjoyed the “varied procedure” and that the endurance group found it “quite boring” to walk continuously during the entire exercise period.

Perhaps most surprising is the age and health status of the subjects. “Of particular interest is the old age of the majority of the patients…, who demonstrated robust training-induced adaptation, even in elderly heart failure patients,” commented the researchers. This “demonstrates that high-intensity training…is feasible” in older patients “with chronic heart failure and severely impaired cardiovascular function.”

Interestingly, only one patient died during the experimental phase, and he was in the moderate-intensity group. The cause of death was found to be “unrelated to exercise training.” (It should be noted that all patients were stable and had not had a heart attack in the last 12 months.)

Let’s take a quick look at another study comparing interval and continuous training, and then we’ll talk about “supercharging” the South Beach Diet.

Intervals Reverse Metabolic Syndrome

Another study from Norway, reported in Circulation (July 7, 2008), compared moderate and high intensity exercise for increasing aerobic capacity (VO2max) and treating metabolic syndrome: a cluster of disorders representing a major risk of coronary heart disease (http://www.cbass.com/SyndromeX.htm).

According to the researchers, individuals with metabolic syndrome (high blood pressure, high cholesterol, elevated blood sugar, and abdominal obesity) are three times more likely to die of heart disease than healthy people.

As in the previous study, aerobic interval training (90% of heart-rate maximum) proved more effective than the same volume of moderate continuous exercise (70% of max). Intervals increased VO2max by 35%, compared to 16% for continuous training. This is significant, because individuals with metabolic syndrome usually have reduced fitness. Intervals also did a better job of removing or reducing the risk factors—probably due at least in part to the greater increase in VO2max.

Interestingly, the researchers gave a clear rationale for interval training: “Most evidence suggests that it is the pumping capacity of the heart that limits VO2max and [intervals] enable patients to complete short work periods at higher intensities, which thereby challenge the pumping ability of the heart more than would be possible [with] lower intensities.”

The study included 32 adults (average age 52) with three or more of the metabolic syndrome traits. As in the previous study, they exercised three times a week,  doing either four 4-minute high-intensity intervals (with three minutes of active rest) or 47 minutes of continuous moderate walking on an “uphill” treadmill. The difference was that the experimental period was longer, 16 weeks compared to 13 weeks. Again, exercise time was calculated to burn the same number of calories.

To cut through the technical nature of the report, the following summary of results is drawn in part from a press release from the American Heart Association (publisher of Circulation).

While both groups experienced a reduction in blood pressure and lost about the same amount of weight, the interval group showed more improvement in how their bodies handle blood sugar and respond to insulin. In addition, the interval group increased HDL “good” cholesterol by about 25%, while the continuous training group showed no improvement.

In typical scientific understatement, the researchers concluded that “these findings may have important implications for exercise training in rehabilitation programs…We propose that high-intensity exercise training programs may yield more favorable results [for patients with metabolic syndrome] than programs with low to moderate intensities”

Now, let’s look at the supercharging of the celebrated South Beach Diet.

Intervals Come to South Beach

Dr. Agatston had heard about interval training for athletes, but until recently he “was unaware of its potential for the rest of us.” His collaborator on The South Beach Diet Super Charged (Rodale, 2008), Joseph Signorile, PhD, an exercise physiologist, told him he could “burn more calories and achieve a higher level of fitness in a shorter period” with interval training. After reviewing the scientific literature and experimenting on himself, he became “convinced that interval training for nonathletes was an important advance.”

Won over, he tells his readers that “conventional wisdom is wrong.” What we’ve been told, he explains, about keeping heart rate around 60% of maximum for at least 20 minutes to burn fat is “simply not true.”

“An abundance of good science supports interval training as a great way to burn fat and calories,” he writes. “Research also shows that it provides better results than working at a constant moderate pace for longer periods,” he adds.

You not only burn more calories and fat doing high-intensity intervals, says the doctor, you also continue to burn more calories “long after the exercise.”

Finally, he explains that interval training is “more effective for normalizing blood sugar and correcting bad blood fats…making it ideal for cardiovascular health.” What’s more, “it’s particularly effective for burning away…the dangerous visceral fat.”

Dr. Agatston tacks on an important warning: “Intense interval training isn’t for everyone. It must be customized for people with certain orthopedic problems or serious heart conditions.”

That’s good advice, of course. As we’ve seen, intervals are good for almost everyone. Check with your doctor if you are new to serious training or have health problems. Start slowly, in any event, and gradually increase the intensity of the intervals as your fitness improves.

(You’ll find interval training programs in Dr. Agatston’s new book, and in our books Ripped 3, Lean For Life, Challenge Yourself, and Great Expectations http://www.cbass.com/PRODUCTS.HTM.)

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