Using High Intensity Interval Training (HIIT) to efficiently burn fat and build muscle

The holiday season has just passed and if you’re like most people you’ve been indulging on heavy foods and have gained a few pounds. You may feel sluggish and tired and you might have made a New Year’s resolution to become more health conscious and exercise more. You might make this resolution with the best intentions only to get bogged down in the New Year by an ultra heavy work-load dumped on you by med-school faculty and by the cold winter days Pittsburgh loves to generate that help quell any motivational fire to get one’s gluteus maximus into the gym.

One of the best solutions to combat these forces and help you get back into shape is High Intensity Interval Training (HIIT). What’s so great about HIIT you say? In the past exercise experts use to support long continuous moderate exercise (CME) as the most effective way to lose weight. This was based on the fact that when they measured calories burned while training CME would beat HIIT. However they failed to see the whole picture and when one measures total calories burned over an entire 24-48hours after an exercise session an HIIT session will beat CME. Why? There are many proposed reasons for this.

When one works out CME style the body rapidly adapts and achieves a steady-state whereby it minimizes calorie-utilization, while HIIT on the other hand, creates a variable state that constantly challenges the body not allowing it to enter an equilibrium making the body require more calories to burn. A second reason is that the high intensity of HIIT causes the body to approach and surpass its aerobic threshold causing it to become anaerobic.

It has been proposed that this switchover from aerobic to anaerobic metabolism (which increases lactic acid production and skeletal muscle micro trauma) is a major stimulus to our hormonal systems to increase output of so-called “youthful hormones” such as testosterone and insulin like growth factor-1 (IGF-1) and other metabolic changes (increased lipid oxidation/utilization and enhanced mitochondrial function) which help your body build more muscle and burn more fat. This hormonal/metabolic adaption helps contribute to the “afterburn effect” of HIIT which is the increased utilization of calories that occurs up to 72hrs post-exercise.

Continued HIIT training will cause long-term up regulation of your basal metabolic rate allowing your body to burn more calories even while you’re sleeping. Our daily activities only account for 15-30% of our daily caloric expenditure while our BMR (the amount of energy required to keep the body functioning) accounts for up to 60-75% of our total energy expenditure. CME does not have a significant afterburn effect and only modestly increases your BMR and this is why HIIT will burn significantly more calories over CME especially when one measures calorie utilization over a prolonged period of time.

CME can help one lose weight but it takes a lot of time to do; 30-60 minutes in order to get any significant calorie utilization, has little to no afterburn effect and is not a major stimulus for long term youthful hormonal production or significant positive metabolic adaptations. In fact it has been shown that frequent bouts of long CME type workout’s over the course of a few weeks can actually create a decrease in one’s testosterone/cortisol levels making it even harder to lose fat and gain muscle. These reasons are why it’s so hard to lose a significant amount of fat and reshape your body with CME style training. That’s why when one starts a CME type program and has the body-type of a large pear at best by the end of 6 weeks or so they will be a slightly smaller pear because CME lacks the ability to truly reshape your body.

HIIT can help one not only lose fat but also build muscle and totally reshape your body all in ½ even ¼ of time that one would train with CME. So if you are ready to make the most of your cardio workouts here are some guidelines to make HIIT work for you:

1. Week 1: Begin your first week by slowly building up your stamina in a traditional CME like style. Try to get in a cardio session 5X the first week and gradually buildup the time of each session. For the first session, train for 10min and workout at a pace at which you could barely hold a conversation with another person. Increase each session by 5 minutes so by the 5th session you are working out at 30minutes. The purpose of this week is to quickly build up your stamina and create a solid base to begin your HIIT program.

2. Week 2: Now that you have built up a cardio platform you can cut your total workout time down to 20minutes a session and inject two 30 sec high intensity sessions within each workout. Example: warm-up for 2.5min then go to a CME like pace for 2.5min then blast up to high intensity for 30secs then back to a CME like pace for 5 min then blast up to high intensity for 30 secs then CME for 6.5 min then 2.5min cool-down. Do this workout 3X a week.

3. Week 3: Begin to increase the number of 30sec high intensity sessions to your workout. As you do this, you’re in between CME like pace can be increased as well as you are getting into better shape. I find that once you get up to 3-5 high intensity sessions with a high CME pace in between one can workout for 15min 3X a week and achieve fantastic results.

Of note: Almost any cardiovascular exercise can be done in an HIIT like style. Ex. walk-jog-sprinting, slow-med-intense biking, slow-med-intense elliptical training, etc… Also remember HIIT can be done in hundreds of different ways the above guidelines are meant to be just that; guidelines to help get you started. Please feel free to adapt/change them as you see fit.

Online References/Resoures:

1. NY Times: A Healthy Mix of Rest and Motion

2. Banda Performance: Females and Strength Training

3. ABC Bodybuilding: Testosterone as a Mediator of Muscle Tissue Growth

Other references:

1. Tabata, I., Irishawa, K., Kuzaki, M., Nishimura, K., Ogita, F., and Miyachi, M., Metabolic Profile of High-Intensity Intermittent Exercises. Medicine & Science in Sports & Exercise, 29(3), 390-395, 1997).
2. Tremblay, A., J. Simoneau, and C. Bouchard, Impact of Exercise Intensity on Body Fatness and Skeletal Muscle Metabolism. Metabolism.43:814-818, 1994.

Dr. Michael B. Mantz

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