By Dr. Mercola
You've probably heard that high-intensity interval training (HIIT) can significantly cut the time needed in the gym, but just how little can you get away with? Could you actually get fit in as little as six minutes per week? The featured ABC Catalyst program investigates this claim.
A significant piece of the puzzle relates to how HIIT affects your mitochondria, tiny organelles found in most of your cells, responsible for production of energy in the form of adenosine triphosphate (ATP).
Your mitochondria have a series of proteins in the electron transport chain, in which they pass electrons from the reduced form of a metabolized portion of the food you eat to combine it with oxygen from the air you breathe and ultimately form water. As noted in the featured program, the more mitochondria you have and the healthier they are, the more energy your body can generate and the lower your risk of chronic disease.
Disturbingly, research suggests half of people under the age of 40 have early onset mitochondrial dysfunction, which is one of the primary contributors to virtually all chronic degenerative disease, like cancer, heart disease, diabetes, arthritis and Alzheimer's. The good news is, studies also show HIIT is very effective for boosting mitochondria and improving their function — and that results can be gained incredibly fast.
Fit in Six Minutes a Week
Your over 1 quadrillion mitochondria comprise an estimated 10 percent of your total body mass, so they make up a significant portion of your body and produce your body weight in ATP every day. In addition to generating ATP, your mitochondria are responsible for apoptosis (programmed cell death), and also serve as important signaling molecules that help regulate the expression of your genes. This is a function that even most doctors are unaware of.
Aerobic fitness is determined by measuring the amount of oxygen your mitochondria can consume when you push yourself to the limit, a measurement called VO2 max. The lower your VO2 max, the higher your risk of chronic diseases such as diabetes, heart disease, cancer, Alzheimer's and more, and the higher your VO2 max, the greater your level of fitness and general health.
Top athletes typically register in the 60 to 70 milliliters per kilo (2.2 pounds) per minute (mL/kg/min) range. The ABC reporter tested her VO2 max at the outset of her 15-week program, scoring a measurement of 36 mL/kg/min, which is a high average.
The conventional recommendation is to get 150 minutes of moderate exercise each week. The problem is most people simply do not have that kind of spare time, and thus end up not exercising at all. But in recent years, scientists have demonstrated you can make great fitness gains in a fraction of that time.
Three Minutes of HIIT Is as Effective as 150 Minutes of Moderate Exercise
A 2016 study1 involving three groups of exercising men — a control group, a group doing sprint interval training and a group doing moderate-intensity continuous training (MICT) — underscored the value of HIIT.
After 12 weeks of workouts, the researchers concluded that three minutes of interval sprints per week (totaling 30 minutes in the gym) was as effective as 150 minutes of MICT, improving insulin sensitivity, cardiorespiratory fitness and the mitochondrial content in skeletal muscle to the same extent.
HIIT also triggers mitochondrial biogenesis,2 which is important for longevity. By reversing age-associated declines in mitochondrial mass, you effectively slow down the aging process. As you'll see later, this even includes some of the more visible signs of aging. As explained in my new book, "Fat for Fuel," because mitochondrial dysfunction seems to be at the core of most chronic disease, activities like HIIT that support mitochondrial biogenesis will strengthen your body and help it fight the ravages of time.
Just be sure to allow ample recovery time between workout sessions because as intensity increases, frequency needs to diminish. Doing HIIT more than three times a week can be counterproductive.
Intensity Is the Key
The key that opens the proverbial door to all of HIIT's health benefits is to make sure the intensity is high enough. McMaster University exercise physiologist Martin Gibala, who has led many HIIT studies, describe the intensity required as "sprinting from danger-kind of intensity."
In other words, you need to give it all you've got, but only for about 30 seconds, repeated four to six times with a minute or so recovery time in between sprints. Your actual exertion time ends up totaling just two to three minutes per workout session.
In one HIIT study, participants increased their endurance capacity by 50 percent on this kind of program. Typically, your VO2 max will improve by 10 to 15 percent in as little as a few weeks. Blood pressure and body composition also typically improves in that short amount of time.
The improvement in VO2 max is largely dependent on the adaptation of your mitochondria. They're what allows your body to process greater amounts of oxygen, resulting in greater energy production and thus power, strength and endurance.
Not only does HIIT boost the number of mitochondria in your cells, it also improves their function and replaces old, worn-out mitochondria with new, better-functioning ones. Tests reveal subjects were able to increase mitochondrial function by 30 percent in as little as one month of HIIT.
While the above information represents the current conventional view on the value of intense exercise, I have learned that it needs a radical revision to optimize long-term health.
A far wiser approach would be less intense exercise more regularly. I describe my current view on intense exercise in the last section, and have a video to expand on it. Rather than going all-out two to three times a week, it is far more rational to do it two to three times every day for three minutes. I am convinced that spreading the exercise out over time is more beneficial.
Exercise Can Slow or Even Turn Back Your Biological Clock
Researchers are also honing in on the mitochondria's influence on the aging process itself. It stands to reason that the two are linked. Indeed, one of the reasons your skin sags and wrinkles with age is because of the loss of mitochondria in your skin. Interestingly, HIIT may even reverse these superficial signs of aging. Mice genetically bred with a faulty mitochondrial system have only half the life span of regular mice; have thin, weak muscles, and develop gray hair and wrinkled skin very early on in life.
When these mice exercised at a brisk pace three times a week, all of these symptoms of mitochondrial dysfunction were eliminated, including the premature graying and skin wrinkling. Human tests have produced similar results.
In one test, skin biopsies were taken from sedentary seniors before and after three months of endurance training. After three months, their skin samples were indistinguishable from much younger skin under the microscope. The exercise basically turned back the clock by as much as 30 years.
As noted in the program, this does not mean all of their wrinkles vanished, but the dead skin layer thinned, and the layer of collagen fibers thickened. It's conceivably possible to dramatically reduce the number of wrinkles you end up with in old age by maintaining an exercise program throughout your life, thereby preventing the breakdown of mitochondria in your skin in the first place.
Exercise physiologist Stephen Boutcher, featured on the show, is also using a modified HIIT program to address menopause and the visceral fat accumulation that tends to go hand in hand with the loss of estrogen.
The women taking part in his program do eight-second sprints at very light resistance, with 12 seconds of light pedaling in between sprints. After 20 minutes, they have sprinted for a total of eight minutes. All of the participants report feeling better. Some have completely eliminated their hot flashes and night sweats, for example.
What Fitness Gains Can You Get From Four Months of HIIT?
The ABC reporter in the program did four 30-second sprints, three times a week for four months, equating to just six minutes of all-out exercise per week. What fitness gains did she reap? Here's what her follow-up tests revealed:
- Body fat went from 26.6 percent to 25.1 percent
- In all, she lost 3.5 pounds (1.5 kilos) of body fat (mostly from her lower trunk and upper legs) and nearly 2 inches (5 centimeters) from her waist
- VO2 max increased by 10 percent, from 36 mL/kg/min to 40 mL/kg/min, moving her into the "fit" category
- Her endurance dramatically improved, from barely being able to complete a 3-kilometer (1.86-mile) jog to comfortably running 9 kilometers (5.59 miles)
HIIT Works Best for Aging Muscles
While many still believe intense exercise is a recipe for a heart attack, research negates such worries. In fact, HIIT is suitable even for the elderly. In a study by Mayo Clinic researchers, three types of exercise were pitted against each other and a non-exercising control group, to determine which type of exercise works best to protect aging muscles.3 HIIT was a clear winner.
The study involved 72 sedentary people aged either 30 or younger or 64 and over. They engaged in 12 weeks of HIIT on stationary bikes, vigorous resistance training or a combination of exercises (moderate pace stationary bike combined with light weightlifting). All of the exercisers experienced improvements in lean body mass and insulin sensitivity, and those who engaged in resistance training had boosts in muscle mass and strength.
Among the HIIT group, improvements in endurance were particularly noted. However, additional notable differences were revealed when the participants' muscle cells were biopsied, revealing genetic changes. Among the younger exercisers, the HIIT group had changes in 274 genes, compared to 170 genes for the moderate combination exercisers and 74 among the resistance group.
The changes among the older exercisers were even more striking. In the elderly, nearly 400 genes were upregulated, compared to 33 for the resistance group and only 19 for those doing moderate exercise, and many of the genes affected specifically influence mitochondria's ability to produce energy for muscle cells.
Boost Your Health With the Nitric Oxide Dump
I now believe one of the best high-intensity exercises is the Nitric Oxide dump that I demonstrate in the video above, which is a modified version of one developed by Dr. Zach Bush. If you have previously watched this video, please review it again as it has been edited to show you how to perform this exercise properly. I do this exercise two to three times virtually every day, unless my schedule is massively overbooked.
I use 8-pound weights in the video but it's best to forgo the weights when you first start out. The whole routine takes about three to four minutes and is typically done two to three times a day every day, with at least two hours between sessions.
I am now convinced that this gentler strategy, which has not been evaluated or compared to the HIIT protocols discussed above, is a far healthier strategy to obtain the benefits of HIIT without the downside. I only wish I had known about this more effective approach earlier.
As noted in the featured program, mitochondrial decline with age is closely linked to reduced cardiorespiratory fitness, and decreased resting mitochondrial ATP production may be involved in the development of insulin resistance with aging.4
Exercise promotes mitochondrial health by forcing your mitochondria to work harder. One of the side effects of mitochondria working harder is that they're making reactive oxygen species, or free radicals, which act as signaling molecules. One of the functions they signal is to make more mitochondria. So, when you exercise, your body responds by creating more mitochondria to keep up with the heightened energy requirement.
Aging is inevitable, but your biological age can be quite different from your chronological age, and your mitochondria have a lot to do with your biological aging. As noted in this program, HIIT appears to be an excellent way to boost the number of mitochondria in your body and improve their function.
The end result is improved body composition and cardiometabolic health, and research shows it's really never too late to start. Some of the studies discussed in the program involved people in their 70s, and even at that advanced age they were able to achieve significant health improvements.