px-r-F5cPQX9ZxUrwgORsMGDGwU Kuhnesiology: Now that you're sick of turkey...

Tuesday, December 13, 2011

Now that you're sick of turkey...

So sorry for the delay.  I have been putting off finishing this...using the "finding a new car because my civic was totaled" excuse.  That excuse has worn itself out.  

I hope everyone had an awesome Thanksgiving.  I was fortunate to visit family and friends I had not seen in ages.  I've been asked by a few different people how hard (either by heart rate or rating of perceived exertion) they need to exercise to burn the most fat...especially after a 5000 calorie "meal" (estimated average Thanksgiving meal caloric intake).  So the question is...to burn the most fat or to lose the most weight..."What is the ideal fat burning zone (IFBZ)?".

I have major issues with this question for a few specific reasons.  Before I get into my objections to the "ideal fat burning zone", I'll go into some basics of bioenergetics.    

In order for any muscle contraction to occur, energy must be freed from  ATP (adenosine triphosphate).  When one of the high energy phosphate bonds is broken from ATP, changing it to ADP (adenosine diphosphate), energy is freed up to allow muscle contraction to take place, and thus work can be done.  There exists in each muscle cell a very limited supply of ATP (roughly enough for 10 seconds of maximal intensity exercise).  Once this "fuel" is used up, the body can use 3 macronutrients to produce more ATP:  carbohydrates, fats, and protein.  I will focus primarily on the first two.  At any given time, the body is using a percentage of carbs and fats to produce ATP through different metabolic mechanisms.  The specific ratio of these two macronutrients is directly related to how intense the exercise is.  The more intense the exercise, the higher the percentage of carbohydrates used to produce ATP.  Conversely, the lower the intensity of exercise, the higher the percentage of fat used to produce ATP.  Generally speaking, the higher the intensity of exercise, the shorter the duration of activity, and vice versa.  

Individuals seeking to lose weight typically are not as concerned with the number of calories used, but the amount of fat they lose, as determined by their scale.  Due to this, the traditional thinking is to focus on exercises that "burn" the most body fat.  So...based on this premise...it makes sense that one should be doing low intensity exercise since this would result in a higher percentage of fats versus carbohydrates used to produce ATP.  It is from this idea that the "ideal fat burning zone" has become so popular.                           
There are various equations and calculations, along with specific products, such as Newleaf, employed to figure out an individual's IFBZ.  Since heart rate is closely linked to exercise intensity, this is the most common measure used to find the IFBZ.  So...the IFBZ is the specific range (typically heart rate) at which the amount of fat, measured in calories, peaks.  D.G. Carey explains this in his article, which can be viewed here (http://www.ncbi.nlm.nih.gov/pubmed/19855335).

This seems like a great thing to know for someone wanting to lose weight...but I personally do not use this when training clients seeking to lose weight.  I believe there are better ways to expend both total calories and the amount of fat "burned".  Before I discuss what method I typically employ for weight loss, I'll explain why I don't think IFBZ isn't all it is cracked up to be. 

The major problem I have with IFBZ is that maximal fat oxidation occurs around 54% of VO2 max, according to the D.G. Carey and the article cited earlier (http://www.ncbi.nlm.nih.gov/pubmed/19855335).  According to Dr. Howard LeWine, this roughly equates to about 7-8 food calories burned per minute during exercise and typically matches up to about 70% of an individuals heart rate max (http://www.intelihealth.com/IH/ihtIH/WSIHW000/35320/35322/423294.html?d=dmtHMSContent).  So...at the IFBZ...the amount of time necessary to burn a sufficient number of calories for legitimate body fat loss is...well...ALOT.  
Before deeper investigation, I believed that the number of calories burned immediately following low intensity exercise and high intensity exercise were drastically different.  Regardless of the type or intensity of exercise, the body uses primarily aerobic mechanisms (using fat as fuel) to return the body to a state of homeostasis, or recovery.  The excess post-exercise oxygen consumption (EPOC) required to bring the body back to homeostasis is directly related to the exercise intensity and duration.  The higher the intensity, the more calories are required to bring the body to a "resting" level.  However, the same is true regarding exercise duration.  A study performed by J. Laforgia, R.T. Withers, and C.J. Gore has actually shown that the amount of calories burned due to EPOC when comparing high and low intensity exercise bouts, though the percentages were significantly different, were not practically significant (http://www.ncbi.nlm.nih.gov/pubmed/17101527).  So basically regardless of exercise type...some fat calories will be used to return the body to "normal".        

Sorry for that bit of a rabbit trail.  Back to the point...

IFBZ is one way to elicit weight loss, however, I believe that high intensity interval training (HIIT) is a much more efficient way of achieving weight loss...and it provides a few other benefits as well!

HIIT has been used as a training tool for much longer than I've been alive, specifically for sports performance.    It's effects on both athletic performance and weight loss have been researched, but its application to weight loss is only now becoming popular and a "buzz word" in the fitness industry.  I'm not completely sure why this is, so I won't even begin to explain why.  I will be a bit of a "prophet" and say it will be very much a fad in the fitness industry in the very near future.  I'm calling it right now...HIIT is the next "step aerobics."

So what is HIIT exactly?  Well, it is exactly that described by its name...High-intensity intervals.  From a work to rest ratio stand point...it is on the other side of the spectrum with regards to traditional "weight-loss" aerobic exercise.  Instead of a lower intensity "steady-state" cardio-type exercise bout, HIIT involves short, but very intense (perhaps even maximal effort) bouts of exercise paired with short rest intervals...typically to exhaustion.

The reason I prefer HIIT for weight loss comes from the outcome of multiple studies comparing the two forms of training.  Just one example of this comes from a classic study conducted by A. Tremblay, J.A. Simoneau, and C. Bouchard at the Physical Activity Sciences Laboratory at Laval University in Quebec, Canada (http://www.ncbi.nlm.nih.gov/pubmed/8028502).  The study, executed all the way back in 1994 examined head to head 20 weeks of cardio (endurance training:  30-45 minutes of continuous cycling at 60-85% of heart rate reserve) versus 15 weeks of high intensity interval (they called it "intermittent":  10-15 bouts of 10-30 second intervals or 4-5 bouts of 30-90 second intervals with enough rest to return the heart rate to 120-130 bpm) training on measures of body fat (measured using skinfold calipers) and skeletal muscle metabolism (measured by levels of citric acid cycle markers, muscle glycolytic enzymes, and HADH).  As one would assume,  the endurance training resulted in over double the total calories burned during exercise when compared to HIIT...


when it came to the skinfold measurements...the HIIT group experienced fat loss 9 times greater than the endurance training group.  Muscle biopsies revealed that both groups experienced increases in citric acid cycle enzymatic activity, which is indicative of increases in fat metabolism.  More interesting than this finding is that the HIIT group experienced increases in muscle glycolytic enzyme activity (while there was no significant change in the endurance group) as well as a significant increase in HADH (a marker of beta-oxidation...or fat metabolism).  The drastic increase and adaptation in metabolic enzymatic activity results in more fat available for use once exercise is finished...and that over time, HIIT results in more fat burned during normal activity.

So put plainly... when used consistently, HIIT causes more adipose tissue (fat) to be available as fuel.  The more fat used throughout the day...the more is lost over time.  

My favorite HIIT protocol (Tabata http://www.tabataprotocol.com/) is one I learned from my strength and conditioning mentor while in grad school.

The original study on Tabata Protocol was performed by I. Tabata, K. Nishamura, M. Kouzaki, Y. Hirai, M. Miyachi, and K. Yamamoto in 1996 at the National Institute of Fitness and Sports, in the Department of Physiology and Biomechanics at Kogashima Prefecture, located in Japan (http://www.ncbi.nlm.nih.gov/pubmed/8897392).  Izumi Tabata,  the lead investigator, explained that the 7-8 sets of 20 second exercise bouts at 170% of VO2 max with 10 seconds rest between sets results in improvements in both aerobic (14 % increase in VO2 max!!!) as well as anaerobic fitness (28% increase in anaerobic capacity!!!).  This is ridiculous because a moderate intensity endurance training group used in the study to act as some what of a control group only had an increase of 10% with regards to aerobic fitness as measured by VO2 max...and no significant increase in anaerobic capacity.  Izumi Tabata is therefore correct when he said in regards to only 6 weeks of Tabata Protocol that "...The fact is that the rate of increase in VO2 max is one of the highest ever reported in exercise science."    
So...to sum it up in some simple bullet points:

 -HIIT was found to be 9 x more effective at fat loss when compared to traditional cardio-training.
 -HIIT (specifically Tabata) improves VO2 (measure of aerobic fitness) greater than cardio-training.
 -HIIT (specifically Tabata) improves anaerobic capacity (measure of anaerobic fitness) while cardio-training has no significant effect on anaerobic capacity.

I hope I have shown that HIIT is not only better for fat loss, but from a sport performance/health point of view, it is more time efficient and effective for most, if not all, athletic/health/performance goals.

So go ahead and give Tabata Protocol a try.  My favorite piece of equipment to use is a rowing machine, but this protocol can be done on an eliptical, a treadmill, or just about any other piece of equipment.  Try easing into it, going near maximal effort for 2-4 cycles of 20 seconds of work and 10 seconds of rest.  After a few of these sessions per week for a few weeks, bump up to 4-8 cycles.  You'll probably hate all the work...but you'll love the results!

Thanks again for reading!!




  2. i'm loving the blog! keep em comin!