Short Bursts of Exercise Are Better Than Exercising Nonstop

Short Bursts of High-Intensity Exercise

Story at-a-glance -

  • People with diabetes who walked continuously for one hour had no improvements in blood sugar, while interval walkers, who alternated three minutes of brisk walking with recovery walking, improved blood sugar disposal by 20 percent
  • Past research has found that interval walkers also enjoyed more weight loss and lower cholesterol levels compared to continuous-paced walkers
  • Another study found that middle-aged adults were able to improve their insulin sensitivity and blood sugar regulation after just two weeks of interval training (three times a week)
  • High-intensity interval training (HIIT) produces a tremendous boost in human growth hormone (HGH), aka the "fitness hormone," and is linked to improved fitness, insulin sensitivity, and blood sugar control
  • When you use HIIT, your workouts need only be a fraction of the time of continuous workouts, and you typically only need to do them a maximum of three times a week (and possibly less)

By Dr. Mercola

When you exercise, are you the type who jogs or uses an elliptical machine at a slow or moderate pace for a good 30 or 45 minutes -- and maybe even reads a book or magazine at the same time? Or are you a devoted walker who can easily spend an hour or more fitting in your daily walk?

First, I’d like to commend you on your exercise efforts. You are making an investment in your health that will pay you handsomely, both immediately and in the future.

However, there’s something you should know. Exercise experts are quickly abandoning the old exercise advice – the recommendations that suggest you need 30 or 60 minutes of moderate-intensity activity to best stay in shape.

Study after study is showing that this is not the best way to exercise, both in terms of its health benefits and its duration. You can actually reap much greater benefits by exercising in short, high-intensity bursts known as intervals than you can exercising for longer periods at a slower steady pace.

If this is the first you’re hearing about this, listen up: by making a few specific changes to your exercise routine, you can cut your workout time considerably while getting far better results.

Interval Walking Improves Blood Sugar While Continuous Walking Does Not

New research put the concept of interval training to the test against continuous walking for the purpose of improving blood sugar control in people with type 2 diabetes. Exercise is crucial if you have diabetes, but the study showed that how you exercise can drastically change your results.

Study participants were divided into two groups -- one that walked continuously at one pace for an hour and another that walked three minutes briskly, followed by three minutes at a slower pace, repeated for one hour. The researchers expected to see improvements in blood sugar control among both groups, but this wasn’t the case.

The steady walkers had no improvements, while the interval walkers improved blood sugar disposal (your body’s ability to move sugar out of your bloodstream and into areas where it can be used as fuel) by 20 percent.

They also had lower A1C levels, which is a marker of longer-term blood sugar control.1 The increased intensity is important, because your muscles require more glucose to perform high-intensity activity. As one of the study’s authors noted:2

"It's this switch between the intensities that we think is critical here… You're able to work hard, and then rest hard... rather than just walking at a fixed pace."

It’s not only people with diabetes who stand to benefit from interval training, of course. Dr. Michael Mosley, author of Fast Exercise: The Simple Secret of High-Intensity Training 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. Past research has found that interval walkers also enjoyed more weight loss and lower cholesterol levels compared to continuous-paced walkers.3

I recently interviewed Dr. Mosley and it will be running on the site in the next month or so. He wrote the following 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.”

Work Out Harder, Not Longer

Exercising at very high intensity interspersed with periods of moderate rest, a program known as high-intensity interval training (HIIT), is simply one of the best ways to get in shape, in part because it produces a tremendous boost in human growth hormone (HGH), aka the "fitness hormone."

One of the best parts is that the workouts are considerably shorter than you're probably used to and involve as little as four minutes of intense activity combined with rest for a total workout of only around 20 minutes.

Research presented at the Integrative Biology of Exercise VI meeting in Colorado, for instance, demonstrated that high-intensity interval training (HIIT) burns more calories in less time – a mere 2.5 minutes, divided into five 30-second sprint intervals at maximum exertion, each followed by four minutes of light pedaling to recuperate, can burn as many as 220 calories.4

Another study published in the Journal of Obesity reported that 12 weeks of HIIT not only can result in significant reductions in total abdominal, trunk, and visceral fat, but also can give you significant increases in fat-free mass and aerobic power.5

Other research published in the journal Cell Metabolism showed that when healthy but inactive people exercise intensely, even if the exercise is brief, it produces an immediate measurable change in their DNA.6 Several of the genes affected by an acute bout of exercise are genes involved in fat metabolism. Specifically, the study suggested that when you exercise your body almost immediately experiences genetic activation that increases the production of fat-busting (lipolytic) enzymes.

Yet another study found that unfit but otherwise healthy middle-aged adults were able to improve their insulin sensitivity and blood sugar regulation after just two weeks of interval training (three sessions per week).7 A follow-up study also found that interval training positively impacted insulin sensitivity. In fact, the study involved people with full-blown type 2 diabetes, and just ONE interval training session was able to improve blood sugar regulation for the next 24 hours!8 For a quick glimpse of what HIIT is all about, Greatist has summed it up nicely in the interval training infographic that follows.9

The HIIT Workout I Do Twice a Week

I currently use two forms of HIIT. One is the Peak Fitness method of 30 seconds of maximum effort followed by 90 seconds of recuperation. I personally modified the number of repetitions from 8 to 6 last year, as it was sometimes just too strenuous for me to do all 8. So by listening to my body and cutting it back to 6 reps, I can now easily tolerate the workout and go full out. Another tweak I made is to incorporate Buteyko breathing into the workout, which means I do most of the workout by only breathing through my nose. This raises the challenge to another level. I then finish my Peak Fitness workout with Power Plate stretches, 10 pull ups, 10 dips, and 20 pushups, and call it a day. When you're first starting out, depending on your level of fitness, you may only be able to do two or three repetitions of Peak Fitness.

That's okay! As you get fitter, just keep adding repetitions until you're doing eight. And if six is what your body is telling you, then stop there. If you have a history of heart disease or any medical concern, please get clearance from your health care professional to start this. Most people of average fitness will be able to do it though; it is only a matter of how much time it will take you to build up to the full 8 reps, depending on your level of intensity. For a demonstration using an elliptical machine, please see the video above. Here are the core principles:

  • Warm up for three minutes
  • Exercise as hard and fast as you can for 30 seconds. You should be gasping for breath and feel like you couldn't possibly go on another few seconds. It is better to use lower resistance and higher repetitions to increase your heart rate
  • Recover for 90 seconds, still moving, but at slower pace and decreased resistance
  • Repeat the high-intensity exercise and recovery 7 more times. (When you're first starting out, depending on your level of fitness, you may only be able to do two or three repetitions of the high-intensity intervals. As you get fitter, just keep adding repetitions until you're doing eight during your 20-minute session)
  • Cool down for a few minutes afterward by cutting down your intensity by 50-80 percent. This intense program should only be done two to three times a week to allow your body plenty of time for recovery

Try High-Intensity Strength Training, Too


Many people are not aware that you can use HIIT for strength training, too. High-intensity strength training gives you all the benefits that HIIT provides—including all the cardiovascular benefits—but in addition to that, it also induces a rapid and deep level of muscle fatigue. This triggers the synthesis of more contractile tissue, and all the metabolic components to support it—including more myokines. Myokines increase your insulin sensitivity and glucose use inside your muscles.

They also increase liberation of fat from adipose cells and the burning of the fat within your skeletal muscle. Acting as chemical messengers, myokines inhibit the release and the effect of the inflammatory cytokines produced by body fat. They also significantly reduce body fat irrespective of calorie intake. Ideally, you’d incorporate both versions of high intensity exercises, as they each provide important pieces of the fitness puzzle. For example, you might do conventional HIIT using a stationary bike once or twice a week, and super-slow high intensity weight training once a week—or vice versa, to end up with a total of three high intensity sessions per week.

Remember that as your fitness increases, the intensity of your exercise goes up, and the frequency that your body can tolerate goes down. As a result, you need to continuously customize your program to your own fitness level and other lifestyle issues. As a general rule however, you do not want to do high intensity interval training exercises more than three times a week. High intensity strength training can be done twice a week initially, but as you get stronger you will need more recovery time and eventually drop down to once every 7-10 days. Any more than that and you’ll put your body under too much strain.

You Can Do HIIT in Your Own Home


Dr. Doug McGuff, an emergency room physician, is an expert in high-intensity training as applied to strength training. On Dr. McGuff’s website, DrMcGuff.com, you will find links to an entire YouTube library of workouts, done in various locations—in gyms around the country, and at home, using little more than body weight, dumbbells, kettlebells, and a rubber ball. You can also review the recent interview I had with Dr. McGuff above. Here’s one sample high-intensity strength training workout using only dumbbells and a chin-up bar:

  • With a rubber ball behind your back, hold a dumbbell in each hand, and do a static contraction; keep your hips flexed at 90 degrees and your knees flexed at 90 degrees. Basically, you’re in a sitting position without a chair underneath you and, with a weight in each hand, you simply hold that position statically for as long as you can.
  • Follow this with several very slow deep knee bends (squats). By that time, you’ll be so fatigued that lifting your own body weight will be quite challenging. Do them to failure.
  • Next, use your dumbbells for an overhead shoulder press. Initiate the movement as gradually as you can and then move slowly, pressing the weight upward for 10 seconds or more, and lower it back down over a count of at least 10 seconds. Do not rest at any point. In a short amount of time, you will fatigue your shoulder girdle. Select a weight that you can do 8-10 reps with to failure. If you can do more than 10 reps then you need a heavier weight; if you can’t do 8, you need a lighter weight.
  • Biceps and triceps curls with one weight in each hand.
  • If you have a chin-up bar, do several chin-ups using an underhand grip (palms up), as slowly as you can, until fatigue. If you’re not strong enough to do a chin-up, stand on a chair to reach the top of the bar, and simply hold yourself at the top position for as long as you can.
  • Using an underhand grip puts you in the strongest position for engaging all the muscles of your torso musculature. When your hand is supinated and at shoulder width, you’re using your bicep in its strongest position. If you have your hands out or pronated, you’re actually using smaller muscles; you’re using your brachialis and brachioradialis that are going to be a weak link in that movement and cause you to fatigue prematurely before you’ve challenged the bigger muscles in your torso.
  • Next, do one standard military-style push-up with your body in plank position. Start with arms straight. Go slowly down until your chest almost touches the floor. Then slowly push back up. If you’re strong enough, use a very slow cadence of 10 seconds down, 10 seconds up. If you’re not strong enough, you can do push-ups from your knee, or you can do them up against the countertop, where your entire plank torso is on an incline to decrease the resistance.

Recovery Is Crucial When You Exercise Intensely

Recovery becomes increasingly important as you increase intensity. No matter which HIIT exercise you choose, you typically do not need to do them more frequently than three times a week. In fact, doing so can be counterproductive, as your body needs to recover between sessions. The importance of recovery should not be overlooked, as your body needs time to rebuild itself in order to function optimally. As explained by Dr. Jeff Spencer:

"To achieve the most beneficial effects from your workouts in the shortest time it's essential to understand the concept of total load. Total Training Load refers to the total amount of training 'strain' on the body over time. For example, one single super-hard workout can strain the body as much as several moderate intensity workouts done back to back can.

The Total Training Load can be increased by increasing the number of exercise repetitions, resistance, length of workout sets and by increasing the speed of repetitions and, also, by shortening the rest interval between exercise sets. If the Total Training Load is in excess too long, the body breaks down, and illness, over-training, burnout, and injury occur."

Recovery also includes giving your body the proper nutrients it needs in the recovery phase, as your post-workout meal can support or inhibit the health benefits of exercise. Choosing a  fast-assimilating high-quality protein, eaten within 30 minutes of your workout, will essentially "rescue" your muscle tissue out of the catabolic state and supply it with the proper nutrients to stimulate repair and rejuvenation. 

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