By Dr. Mercola

Over the last several years, researchers have slowly but surely reached the consensus that high intensity interval training (HIIT), which is characterized by relatively short bursts of intense exercise followed by periods of rest, far outperforms conventional aerobic endurance type exercises.

Not only does it beat conventional cardio as the most effective and efficient form of exercise, it also provides health benefits you simply cannot get from regular aerobics, such as a tremendous boost in human growth hormone (HGH), aka the “fitness hormone.”

Perhaps best of all, HIIT requires only minutes, compared to hours, each week. In the featured video, Dr. Michael Mosley, author of Fast Exercise: The Simple Secret of High-Intensity Training, shares his own experiences with HIIT.

The Truth About Exercise

As Dr. Mosley reports in the featured BBC special, groundbreaking research suggests that as little as three minutes of high intensity training per week can produce significant health benefits.

Dr. Mosley was able to improve his insulin sensitivity by 24 percent by putting in a mere 12 minutes of intense exercise per week, for four weeks. Such an effect is truly amazing, and indeed important, as improving and maintaining good insulin sensitivity is perhaps one of the most important aspects of optimal health.

He performed the exercises on a stationary bike. After warming up, he cycled “all-out” for 20 seconds, rested for a couple of minutes, and then gave it his all for another 20 seconds.

The HIIT approach I personally prefer and recommend is the Peak Fitness method of a 50% longer exercise time of 30 seconds of maximum effort followed by less recovery of only 90 seconds for a total of eight repetitions.

When you’re first starting out, depending on your level of fitness, you may only be able to do two or three repetitions, which is perfectly alright. As you get fitter, just keep adding repetitions until you’re doing eight.

About a year ago, I personally modified the number of repetitions I do from eight to six, as it was sometimes just too strenuous for me to do all eight. By listening to my body and cutting it back to six reps, I can now easily tolerate the workout and go full out. Plus, I no longer dread doing it.

I also do alternatives to elliptical now where I will do six sets with a barbell and ten pounds on it and do deadlifts, bent over rows, upright rows, squats, clean and jerks and bicep curls all in rapid succession with no breaks. It is not quite as intense but goes for about 60 seconds and really pushes me metabolically. I also rest for a few minutes until I recover. I think the variety is good.

Another tweak I made is to incorporate Buteyko breathing, which means I do most of the workout breathing only through my nose. This raises the challenge to another level.

There are very compelling reasons for trading your hour-long walk on the treadmill for a 20-minute high intensity routine, and research shows that in this case, less time can indeed lead to a greater payout, if done correctly. As Dr. Mosley writes in his book, Fast Exercise:

“I believe that we have now produced sufficient data to be able to recommend short bursts of high-intensity exercise as a safe and effective alternative to conventional workouts, removing the ‘time barrier’ as an excuse for not exercising.

This will hopefully boost compliance and help people take up an approach that will lead to a healthier way of life. The great thing about HIIT is that it can be done in the workplace or at home without preplanning or missing an episode of your favorite TV show.”

Even Brief Intense Exercise Produces Genetic Changes That Promote Fat Loss

A study published in the journal Cell Metabolism1 in 2012, showed that when healthy but inactive people exercise intensely, even if the exercise is brief, it produces an immediate change in their DNA. While the underlying genetic code in the muscle remains unchanged, exercise causes important structural and chemical changes to the DNA molecules within the muscles.

This contraction-induced gene activation appears to be early events leading to the genetic reprogramming of muscle for strength, and to the structural and metabolic benefits of exercise. Several of the genes affected by an acute bout of exercise are genes involved in fat metabolism. Specifically, the study suggests that when you exercise, your body almost immediately experiences genetic activation that increases the production of fat-busting proteins! Besides lowered body fat, other benefits associated with high intensity interval training include:

  • Improved muscle tone
  • Firmer skin and fewer wrinkles
  • Higher energy levels
  • Improved athletic speed and performance
  • Boosted sex drive

Intermittent Movement—Another Crucial Piece of the Puzzle

In the video, Dr. Mosley also meets with Dr. James Levine, a Mayo Clinic obesity expert whose research suggests that the best way to lose weight is to increase your non-exercise activity thermogenesis, also referred to as NEAT. This is the calories you expend during your day-to-day living, through body movement that have nothing to do with traditional exercise.

Similar research has been conducted by Dr. Joan Vernikos, former director of NASA’s Life Sciences Division and author of Sitting Kills, Moving Heals.

Mounting research clearly shows that undisrupted sitting for long periods of time is an independent risk factor for chronic disease and early death—even if you exercise vigorously each week. More and more, we’re starting to realize the importance of keeping your body in perpetual motion—bending, stretching,  reaching, standing up…

Using so-called “fidget pants,” Dr. Levine measures how much Dr. Mosley and other volunteers move during any given day, and how that non-exercise movement translates into calories burned. As it turns out, even slight increases in daily motion can result in several hundreds of calories burned.

When asked which might be more important for health: intermittent bursts of high intensity exercise a few times a week, or more or less non-stop non-exercise movement throughout the day, Dr. Levine notes that those who exercise regularly will clearly continue to do so because they love it.

But a large section of the population gets no exercise whatsoever and think nothing of it. For those people, paying careful attention to their intermittent movements—the movement inherent in their daily living—becomes incredibly relevant and important for their health. In a nutshell, the key to optimal health is to “keep off your bottom as much as possible.” It’s just that simple. That in no way detracts from the importance or benefits you can reap from a regular fitness regimen though.

According to Dr. Levine, “there should never be an hour where you’re sitting down.” One solution, provided your job can accommodate it, is to do your work standing up. Another solution, suggested by Dr. Vernikos, is to make sure you stand up at least once every 15 minutes or so. In a previous article, I collected a list of 30 videos demonstrating quick and simple exercises you can do when you stand up.

What Makes High Intensity Exercise So Effective

Getting back to high intensity exercise, part of the key that makes HIIT so effective is that it engages far more of your muscle tissue than conventional aerobic cardio exercise. You have three different types of muscle fibers: slow, fast, and super-fast. Only ONE of these muscles, the super-fast fibers, will impact your production of human growth hormone (HGH), which is KEY for strength, health, and longevity. The vast majority of people, including many athletes such as marathon runners, only train using their slow muscle fibers. In fact, neither traditionally performed aerobic cardio nor strength training will work anything but your slow muscles. These are the red muscles, which are filled with capillaries and mitochondria, and hence a lot of oxygen.

The fast type of fiber, which is also red muscle that oxygenates quickly, is five times faster than the slow fibers. Power training, or plyometric burst-type exercises, will engage these fast muscles. The super-fast ones are the white muscle fibers. They contain far less blood and less densely packed mitochondria. These muscle fibers are what you use when you do anaerobic, short burst exercises. High intensity burst-type exercises are the ones that will engage these super-fast fibers. They’re 10 times faster than slow fibers, and activating them is the key to producing growth hormone! To further maximize your growth hormone release, you’ll want to:

  • Get a good night’s sleep
  • Optimize your vitamin D levels
  • Avoid sugar, especially fructose. (If you consume sugar or fructose, especially within two hours post-exercise, you will virtually obliterate the production of growth hormone!)

Tips for Building a High-Quality Fitness Regimen

Ideally, intense exercise should be balanced with strength training, proper stretching, core strengthening, stress reduction, restorative sleep, and good nutrition. You’ll find much more information about HIIT and other types of exercise in the fitness section of my website. When putting together your exercise routine, I recommend incorporating the following:

  1. Stand Up Every 15 Minutes. Compelling research now tells us that prolonged sitting can have a tremendously detrimental impact on your health, even if you exercise regularly. Your body needs to interact with gravity in order to function properly, and this has to be ongoing, throughout your day. Whenever you have a chance to move your body, do so! I invite you to look at our list of 30 videos for ideas about what you can do when you stand up.
  2. Interval Peak Fitness (Anaerobic) Training: Interval training involves alternating short bursts of high-intensity exercise with gentle recovery periods, and are central to my Peak Fitness routine.
  3. Strength Training: Rounding out your exercise program with a one-set strength training routine will ensure that you’re really optimizing the health benefits of your fitness program. You can also “up” the intensity by slowing it down. For more information about using super slow weight training as a form of high intensity interval exercise, please see my interview above with Dr. Doug McGuff, and my video about super slow workouts at the top of this section.
  4. Core Exercises: Your body has 29 core muscles located mostly in your back, abdomen, and pelvis. This group of muscles provides the foundation for movement throughout your body, and strengthening them can help protect and support your back, make your spine and body less prone to injury, and improve your balance and stability. Foundation Training, created by Dr. Eric Goodman, is an integral first step of a larger program he calls “Modern Moveology,” which consists of a catalog of exercises.
  5. Stretching: My favorite type of stretching is Active Isolated Stretching (AIS). With AIS, you hold each stretch for only two seconds, which works with your body’s natural physiological makeup to improve circulation and increase the elasticity of muscle joints. This technique allows your body to repair itself and prepare for daily activity. You can also use devices like thePower Plate to help you stretch.


Here’s a sample HIIT workout that’s simple, but effective:

60 Seconds Sprint/Fast Jog
120 Seconds Walk/Slow Jog

I do this HIIT workout all the time on a treadmill, elliptical, or outside. The duration of “work” is 60 seconds, and my “rest” is 120 seconds. The work/rest ratio in this case is 60/120, or 1 to 2. I shoot for 5-10 cycles, depending on the type of cardio I’m doing and if it’s right after strength training. The better shape you are in, the higher intensity you can handle and the higher the work/rest ratio. For example, well trained athletes can use a 2 to 1 work /rest ratio, so they are sprinting for 120 seconds and only resting for 60 seconds. That’s tough!

Any type of cardio can be used with interval training, but I would caution against running more than a few times per week, because the demands on your metabolic system and joints are significant. For beginners, I recommend the elliptical, which is lower impact. Swimming, jumping rope, cycling etc. can all work well as training modalities.