PT on the Net Research

Myth-busters: Burn more Fat not more time?

Although, all of the information that is presented in this article is geared toward the benefits and/or effectiveness of anaerobic high intensity interval training (HIIT) vs. low intensity aerobic training with regards to fat utilization, there is an understanding that some reasons for aerobic training supersede the outcomes.  For the sake of pure enjoyment, personal goal setting (training for a triathlon, marathon, road race, etc), and the challenge of competition are all viable and respectable reasons for interacting with long slow distance (LSD) activities.  For many people these types of activities are suitable for their lifestyle and enjoyable means of living an active life.  The goal of this article is not to discount or diminish the value of physical activity in all its modalities, but to merely present data with regards to optimum fat loss, hormonal indicators, and other factors of cardiovascular and cardio respiratory markers as they pertain to exercise intensity prescription.

Misinformation is Costing Money

People today are on sensory overload with achieving a “lean or sculpted” physique.  This has made weight-loss a billion dollar industry (46.3 billion to be exact as reported by, 2004). If your clients have ever been to a gym, talked about working out, or even remotely have expressed interest in their health, they have probably had the “I need to lose weight” or “shed a little fat” talk at some point.  Marry this desire with the endless supply of jargon in magazines and infomercials that promise miracles with the use of their products and we see the weight loss industry getting richer and richer.  The unfortunate part is that most people have little or no educational means to differentiate between what is effective and what is merely an elaborate marketing effort.  Oddly enough, there is a gym on virtually every street corner and new weight loss supplements are coming out on a daily basis. Yet, the obesity rate in the US has grown to epidemic proportions.  In 1998 the indirect cost of obesity in healthcare, or sick-care as I like to call it, in the U.S. was $47.56 billion (13).  These numbers alone reflect nearly $100 billion spent in the U.S. to combat obesity!  With this many products and weight loss systems available that claim to give you a rock hard physique or fitness model quality body, how can so many Americans be overweight?  One word, misinformation!

So now that both your mood and pocketbook have been suppressed, how can we ensure that our efforts toward weight loss, and moreover fat loss, are attainable?  The answer is more effective training.  This article is intended to share what has been reported in the scientific literature for decades.  In the following section several myths associated with fat loss will be discussed and debunked. It is important for the reader to understand that the information about to be presented goes beyond the author’s opinion and is based on scientific research, not claims or gimmicks.  So, stop buying supplements that claim you don’t have to work out to lose fat or to be lean.  The only thing they make smaller is your disposable income. You MUST exercise to burn fat effectively. Quit joining the fad diet crazes!  Over half of those people gain back the weight. In fact, many of these diets promote calorie reduction without exercise.  As a result, lean muscle may also be lost in conjunction with fat and causes a reduction in the resting metabolic rate.  Frequently, when people return to their pre-diet weight they are actually fatter in terms of body fat percentage than before they went on the diet.

Get Educated

What is the solution to this endless cycle?  Education. It is time to START LEARNING!  Odds are you did not get your job by ordering a magic pill or following some fanatical routine, so stop treating your health the same way.  If you truly desire to lose weight or to get leaner, you must learn how the body works, even if it is from a crude or rudimentary standpoint.  Otherwise you will continue to waste money on ineffective products and gym fees for the rest of your life!

Here are some facts about why aerobic long slow distance training (LSD) may be less effective and possibly even counterproductive for fat loss when compared to high intensity interval training (HIIT).  First of all, LSD and interval training both increase fat oxidation (burning). However, the positive effect for LSD can take up to two weeks to be effective whereas interval training demonstrates an immediate return.  This is generally due to the nature of glycogen (sugar) depletion.  With HIIT, glycogen is depleted rapidly.  But in LSD training, depletion requires much longer durations as the intensity of exercise is exceedingly lower.  Fat oxidation will markedly increase with depleted glycogen levels.

Does this sound familiar?  This is essentially the basis of the ever so famous “low carb” diet craze.  With depleted glycogen (carbohydrate), the body will initiate higher levels or fat oxidation.  However with this type of diet, protein and/or muscle loss may be affected as well. Glycogen levels are important and all the macronutrients (fat, carbohydrate, and protein) play a significant role in overall nutrition and health.

Fat Burning Zone

Secondly, do not get caught up in the “fat burning zone”.  This is generally in reference to the percentage of heart rate (HR) max.  This has typically been displayed for unsuspecting users of cardio equipment in health clubs.  The typical “fat burning zone” is promoted as being near 65% of HR max.  While there is truth in the statement that at 65% of HR max, a higher level of fat will be oxidized when compared to carbohydrate consumption, the overall training effect utilizes less fat.

Let’s take a closer look at this for caloric burn and also from what is called EPOC, or excess post oxygen consumption.  EPOC generally accounts for the energy expenditure during recovery from the exercise bout or the “post exercise burning" of calories (9).  Typically this EPOC is fueled by fat and the intensity of work performed. The higher the intensity, the higher the EPOC.  When compared to post exercise fat oxidation, moderate to low intensity exercise barely compares.  Take for example the work done by Tremblay et al.  This study compared an aerobic group and an anaerobic group of subjects for caloric burn and fat loss.  The aerobic group trained for 20 weeks while the anaerobic group (interval) trained for only 15 weeks.  The results showed that although the aerobic group burned nearly 50% more calories, the anaerobic (interval) group burned nine times more subcutaneous fat than their counterparts (11).   For those not paying attention, in summary, that is five weeks less work and nine times the fat lost.  Imagine becoming the trainer who is known for giving clients better results in a shorter period of time!

Cellular Hydration

Cellular Hydration is the third point of interest.  There is a surprising thermogenic affect of water.  A study of seven men and women who drank 500 milliliters found that after merely 10 minutes of ingestion the subjects resting metabolic rate rose by 30%.  Interestingly, this influx was fueled by fat in the male subjects and carbohydrate with the female subjects (1).  Typically the rule of thumb for water consumption is near one gallon per day.  Not too many people reach this goal on a daily basis.  Water also aids in nutrient absorption and also helps flush out toxins accumulated from exercise.

Muscle Burns Fat?

The caloric utilization of tissues in the body differs too.  The old adage that “muscle burns fat” is not entirely true.  But when compared, muscle tissue burns 7-10 kcal/kg/day whereas adipose tissue only consumes 2-3 kcal/kg/day.  Look at the figure below.  Which one of these athletes looks the leanest?  Now, which one of these athletes looks like they have more muscle mass?  Lastly, which athlete is a sprinter (high intensity interval) and which do you think is the aerobic (jogging, LSD) runner?  If you guessed the runner on the left, you were correct on all three accounts.

Photo 1 Photo 2

As you can see by the images, the athlete in Photo 1 appears to have a larger percentage of lean mass than does the athlete in Photo 2.  With this statement and the aforementioned data, it seems feasible that the sprinter possesses a higher resting metabolic rate (RMR) as well due to the higher level of lean mass.  In fact, there is an underlying correlation with RMR and fat free mass (FFM).  Although FFM accounts for muscle tissue, bones, and also organ tissues, muscle is the only of these three that can be altered to any varying degree and thus alone contributes to nearly 22% of RMR (2). Some of the additional benefits that the high intensity interval trained may experience in conjunction with increased fat loss include, greater improvements in VO2max, increased growth hormone response (due to lactate accumulation), and positive blood pressure response (4, 5).


The VO2max may seem surprising to those who have been told that the LSD training will elicit the highest level of VO2max.  This too has been shown to reach higher levels with HIIT when compared to moderate intensity exercise.  Tabata et all compared a “fat burning zone” group vs. a HIIT group and found that although the fat burning group improved VO2max by 10%, they did not produce any concomitant improvement in anaerobic capacity.  Conversely, the HIIT group improved their VO2max by 14% and their anaerobic capacity also rose by 28% (10).  Furthermore, a third party University study showed that the 1992 Canadian Alpine ski team (predominately HIIT) demonstrated higher VO2max markers than their Nordic (highly aerobic) counterparts.

Still think that your aerobic work is the ticket to success?  Here are some other contributing factors to think about.  High levels of aerobic exercise increases adrenal stress which can increase the potential for such symptoms as insomnia, depression, reduced memory, frequent influenza and most importantly – the ability to lose weight (12).  Also, aerobic training has an effect on local muscular power (3, 6, 8) and lastly, training aerobically diminishes testosterone/cortisol ratio, which in turn also impedes your ability to burn fat (7).


The traditional school of thought for exercise prescription and fat loss has been long assumed to be accomplished through aerobic activity.  However, with the plethora of research that has been geared toward finding the best means of fat utilization, we now know that HIIT is by far a better method for attaining this goal.  Keep in mind that HIIT is very demanding and that it is important to ensure that your client/athlete is cleared for such activity through a medical professional.  Also understand that the chronological age and training status of your client will determine what might be HIIT for each person.  A 55-year old untrained client will quite easily reach an anaerobic state and for much shorter duration than will a 25-year old moderately trained client.  If these parameters and considerations are kept in mind, HIIT can benefit people from all walks of life and all levels of fitness.


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  2. Bray, GA, Bouchard C, and James W.P.T. (1998) Handbook of Obesity. New York: Marcel Dekker.
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  9. Stainsby WM, and Barclay JK. (1970) Exercise Metabolism: O2 Deficit, Steady Level of O2 Uptake and O2 Uptake in Recovery. Med Sci Sports 2:177-195.
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