By Dr. Mercola
Are you still struggling to fit exercise into your regimen? If so, there's good news: You can exercise less if you pick up the pace. The time required is inversely associated with the intensity. The higher intensity, the less time you have to spend on it.
Years of research have built a scientific consensus, as study after study reveals that exercising in shorter bursts with rest periods in between produces far greater genetic and metabolic benefits than exercising continuously for an entire session.
Can You Get Fit in Three Minutes of Strenuous Exercise Per Week?
As incredible as it sounds, a recent experiment1,2,3 showed that one single minute of strenuous activity within a 10-minute exercise session is as effective as working out for 45 minutes at a moderate pace. If you've put off exercise for lack of time, such findings may be nothing short of life changing.
Twenty-five out-of-shape men in their 30s were recruited for the trial. Their aerobic fitness and insulin sensitivity were measured at the outset of the study. Biopsies of their muscles were also taken, to assess muscular function at the cellular level. The men were then randomly divided into three groups:
- The control group maintained their current exercise regimen, which was virtually nonexistent
- The second group engaged in a 45-minute long endurance workout, riding at a moderate pace on a stationary bike
- The third group was assigned to a HIIT program. After a two-minute warm-up on a stationary bike, they cycled all-out for 20 seconds followed by gentle pedaling for two minutes. These intervals were repeated three times, for a total workout of 10 minutes, but only one minute was actually spent in strenuous exertion
The exercise groups completed three workout sessions per week for 12 weeks. As reported by The New York Times:4
"By the end of the study ... the endurance group had ridden for 27 hours, while the interval group had ridden for six hours, with only 36 minutes of that time being strenuous.
But when the scientists retested the men's aerobic fitness, muscles and blood-sugar control now, they found that the exercisers showed virtually identical gains ...
In both groups, endurance had increased by nearly 20 percent, insulin resistance likewise had improved significantly, and there were significant increases in the number and function of certain microscopic structures in the men's muscles that are related to energy production and oxygen consumption."
Less Time, Identical Gains
The obvious benefit of these findings is that, if you exercise efficiently, meaning short intense bursts of exertion, you can get fit in a mere fraction of the time it would take you engaging in more moderate exertion. And the results — in terms of improving your health and fitness — are virtually identical.
The only thing that differs is the time spent. Think about it; all you need is 10 minutes, three times a week, and you're done.
This is just half of the time I typically recommend, as my program involves going all out for 30 seconds and then resting for 90 seconds between sprints. The total workout is typically six to eight repetitions, which you would complete in 20 minutes or less.
Regardless of which HIIT version you choose, the evidence is quite clear: You can get fit even if you're very pressed for time. As Martin Gibala, Ph.D., a professor of kinesiology who led the study, told The New York Times:
"If you are an elite athlete, then obviously incorporating both endurance and interval training into an overall program maximizes performance.
But if you are someone, like me, who just wants to boost health and fitness and you don't have 45 minutes or an hour to work out, our data show that you can get big benefits from even a single minute of intense exercise."
12 Minutes of Extreme Exertion Outperform Five Hours of Moderate Exercise
Similar findings have been made by other researchers. For example, Izumi Tabata, Dean of the College of Sport and Health Science at Ritsumeikan University in Japan, developed a HIIT protocol that requires just four minutes of exercise, four times a week. The caveat is extreme intensity — too extreme for most, if you ask me.
The Tabata Protocol calls for just 20 seconds of all-out, drop-dead effort, followed by a mere 10 seconds of rest. This intense cycle is repeated eight times. His view is, if you could actually keep going after these four minutes, you're not doing it intensely enough.
When performed four times per week for six weeks, participants in one experiment increased their anaerobic capacity by 28 percent, and their VO2 max (an indicator of cardiovascular health) and maximal aerobic power by 15 percent. Meanwhile, the control group, who performed an hour of steady cardiovascular exercise on a stationary bike five times a week, improved their VO2 max by just 10 percent, and their regimen had no effect on their anaerobic capacity.
Despite the potential benefits, in my view the short interval of rest makes this program far too intense for most people, and I only recommend it for people who are exceptionally fit already and want to take the intensity to the next level.
Suggestions and Considerations
Remember, while your body needs regular amounts of stress like exercise to stay healthy, if you stress it too much, your health can actually deteriorate. Balance is key, so listen to your body and modify your exercise intensity and frequency based on the feedback you get from your body.
When you work out, it is wise to really push as hard as you possibly can a few times a week, but you need to wisely gauge your body's tolerance to this stress.
When you're first starting out, depending on your level of fitness, you may only be able to do two or three repetitions of HIIT, regardless of which program you follow. That's OK! As you get fitter, just keep adding repetitions until you're doing the recommended amount.
If you have a history of heart disease or any medical concern, please get clearance from your health care professional before embarking on a HIIT program.
Most people of average fitness will be able to do it though; it's just a matter of how long it will take you to build up to the full set of reps, depending on your level of intensity. To find the HIIT workout that works best for you, see my previous article: "This Interval Training Infographic Helps You Pick the Right Workout."
What Makes HIIT so Effective and Beneficial?
As mentioned, the higher the intensity, the less time is required. But why is that? High-intensity exercise appears to produce its benefits via a number of different mechanisms. It's quite likely we've not even identified all of them as of yet, but part of the answer has to do with genetic optimization. The human body evolved performing very high-intensity activities for brief periods of time, and this kind of activity appears to be "built into" our genotype.
Research bears this out. For example, a study published in the journal Cell Metabolism5 in 2012 showed that when healthy but inactive people exercise intensely but briefly, it produces an immediate change in their DNA. Intense exercise causes structural and chemical alterations to the DNA molecules within your muscles, and this contraction-induced gene activation leads to the genetic reprogramming of muscle for strength.
However, the benefits do not end there. Other genes affected by intense exercise are genes involved in fat metabolism, which is why HIIT is so effective for weight loss, whereas other forms of exercise often fail to produce any significant results. According to the American College of Sports Medicine,6 HIIT workouts tend to burn anywhere from 6 to 15 percent more calories compared to other workouts.
HIIT also produces a significant improvement in glucose tolerance; far more so than any other form of exercise. In fact, research7,8 has shown that low-intensity exercise tends to produce no such improvements at all. This is a noteworthy difference, as normalizing your glucose and insulin levels is one of the most important benefits of exercise, considering the fact that insulin resistance is a factor in most chronic disease, including diabetes and heart disease.
High intensity is also required in order to trigger the production of human growth hormone (HGH). Your production of vital HGH can increase by as much as 770 percent during a high-intensity interval workout because it stimulates your fast twitch muscle fibers, which are rarely used during most exercise programs. And the higher your levels of HGH, the healthier, stronger, and fitter you'll be.
The Importance of HIIT for Mitochondrial Biogenesis
HIIT also triggers mitochondrial biogenesis, which is important for longevity. In essence, by reversing age-associated declines in mitochondrial mass, you slow down the aging process. As noted in a 2011 review9 in Applied Physiology, Nutrition and Metabolism, exercise alters mitochondrial enzyme content and activity, which helps increase cellular energy production, and in so doing decreases your risk of chronic disease.
For example, one of the universal characteristics of cancer cells is they have serious mitochondrial dysfunction with radically decreased numbers of functional mitochondria.
Increasing mitochondrial activity is extremely important because free radicals, which are toxic byproducts of metabolism as well as exposures to chemicals, pollutants and other toxins, can overwhelm your body's defenses, leading to oxidative damage to cells and tissues that can destroy cellular proteins, lipids and DNA; this process often leads directly to the loss of mitochondrial function.
In the long term, irreversible damage in the mitochondria can occur, leading to impaired ability to utilize carbohydrates and fat for energy, insulin resistance, lowered threshold for physical exercise, weight gain, and accelerated aging.
At least two studies10,11 have also shown that exercise induces mitochondrial biogenesis in the brain, which helps limit (or even reverse) age-associated declines in cognitive function. It can also help repair brain damage following a stroke.12 However, it is important to remember that diet trumps exercise and if you're consuming processed food and excessive net carbs, this will blunt your body's ability to optimize repair and regeneration through mitochondrial repair.
Switch Up Your HIIT Routine With High-Intensity Weight Training
The high-intensity form of strength training, commonly referred to as super-slow weight training, has at least one additional benefit over other forms of HIIT. By inducing rapid and deep muscle fatigue, you trigger the synthesis of more contractile tissue, and the benefit of this includes increased production of anti-inflammatory myokines that have a number of potent health benefits.
Some of the latest research suggest that these myokines — a class of cell-signaling proteins produced by muscle fibers — have a unique ability to combat diseases like metabolic syndrome and cancer.
Now, HIIT performed on a bike or elliptical machine will engage and tax your muscles, for sure, but super-slow weight training really pushes them to the max. So it may be helpful to know that you can indeed get the same, and maybe even better, results by turning your weight training session into a HIIT session if you don't care for sprinting.
It's also a great way to get more variation into your workout routine, as it will challenge your body in different ways. In the video above, I discuss and demonstrate some of the most important super-slow weight training principles.
Core Principles of HIIT
I recommend incorporating both sprint-type and strength training forms of high-intensity exercise into your fitness regimen, although either one will work very effectively without the other. Following is a summary of what a typical HIIT routine might look like using either an elliptical machine or stationary bike:
- Warm up for three minutes.
- Exercise as hard and fast as you can for 30 seconds. You want to get your heart rate up to your calculated maximum heart rate. The most common formula for this is to subtract your age from 220. I highly recommend using a heart rate monitor, as it's very difficult to accurately measure your heart rate without one. A sign that you're giving it enough effort is when you're gasping for breath and feel like you couldn't possibly go on another few seconds.
- Recover for 90 seconds, still pedaling, but at slower pace and decreased resistance.
- Repeat the high-intensity exercise and recovery five to seven more times, for a total of six or eight repetitions, depending on your level of fitness. Remember, when you first start out, you may only muster one or two. Don't fret. Just keep at it and add repetitions as your fitness improves over the following weeks and months.
- Cool down for about three minutes or longer.
HIIT Plus Daily Walking Is a Great Recipe for Health and Longevity
If this is the only type of exercise you're doing, I suggest two to three sessions per week, max. If you're also doing high-intensity strength training, let the strength training session count toward the total HIIT sessions. Avoid doing more than three HIIT sessions per week, as recovery is an important part of the equation.
Last but certainly not least, I also recommend walking more. Ideally, aim for 7,000 to 10,000 steps a day, over and above your regular exercise regimen. Not only will this give your metabolism a boost in the right direction, it's also necessary to counter the ill effects of too much sitting — which in and of itself increases your risk of insulin resistance and metabolic dysfunction, even if you exercise!
The evidence quite clearly shows that standing up more and engaging in non-exercise movement as much as possible is just as important for optimal health as having a regular fitness regimen. Personally, the only time I sit is when I'm driving somewhere.
Other than that, I mostly stand throughout the day, even when working, as I have a standup desk. In my view, a standup desk may be one of the best health investments you could make. I also walk barefoot on the beach for about an hour each day, and if you do nothing else, you could simply turn your walking routine into a high-intensity exercise, cutting your time investment even more. For tips and suggestions, please see my previous article, "How to Turn Your Daily Walk into a High Intensity Exercise."