Running...does it really burn fat?

There is much confusion today on whether or not you are "burning fat" during your run or any other exercise for that matter.  Some articles will tell you you have to exercise at a certain pace to do so, others lead you to believe that if you exercise with the goal of "fat burning" you will lose more weight.  Even exercise machines in the gym have a "fat burning" setting!  With all this talk of fat burning what are you really supposed to do?  Here's the skinny on what all this means...

EXERCISE PHYSIOLOGY 101

Popular culture and media have gotten confused when writing articles pertaining to fat burning during exercise and what that actually means for overall weight loss. 

No matter who you are, what you are doing for exercise, whether you are hopping around on one foot, dancing, playing tag, being silly with your kids or running an actual race the first 20-30 minutes of exercise you are burning sugar for energy.  We store this sugar in the form of glycogen in our muscles.  For the first 60 seconds of exercise we do this anaerobically through two different systems the first being the phosphagen system where we use the hydrolysis of ATP (adenosine triphosphate) and the breakdown of creatine phosphate for energy.  Once we have exhausted our creatine phosphate stores (the basis for which individuals using the ergogenic aid creatine derive their reasoning) we move into what is called anaerobic or fast glycolysis for the production of ATP.  ATP is the basic molecule that has to be present for muscular contraction to occur.  If you exercise at such a high rate that you exceed your lactate threshold performance will decrease.  This will happen around 1 minute at all out high intensity exercise.

After the first 60 seconds of exercise our bodies now have to use oxygen to create the ATP we need for exercise.  We do this through a process of Aerobic or Slow Glycolysis.  We continue to burn sugars with the help of oxygen until we reach approximately 20-30 minutes of exercise.  AT THIS TIME we now start the process of Beta-Oxidation to burn our fat stores known as triglycerides.  This is NOT the adipose tissue that gives you the cellulite appearance!  These are the fat stores in your muscle cells.  Fat burns in a carbohydrate flame.  This is why a diet of 60% carbohydrates is so important for an endurance athlete.  You are still burning sugar and REQUIRE sugar (i.e. carbs) to burn fat to fuel your run.  If you increase your exercise intensity above your lactate threshold at this time you will shift back to primarily burning sugars temporarily but this is NOT sustainable.  Once you deplete your stores you will slow in intensity and return to a pace sustainable through beta-oxidation.   If you can continue to run at your given pace you are burning fat stores until you reach 90 minutes.

At  90 minutes it is only now that you start to burn protein for the production of ATP.  Our bodies have to mobilize proteins from our liver and go through the process of gluconeogenesis to convert the protein into ATP.  After you have exhausted your protein stores from your liver your body at this time will start breaking down other body tissue for protein such as muscle.  This is precisely why high protein diets are not recommended for athletes, especially endurance athletes.

So here we have it:

1.  The first 20-30 minutes of any exercise you are primarily burning sugar stores called glycogen to fuel your workout.

2.  Once you reach 20-30 minutes of exercise you start burning fat for energy.  The fat you burn during exercise is in the form of triglyceride stores in your muscle cells.  This doesn't convert directly into weight loss.

3.  Weight (body fat) loss occurs when you have a caloric deficit at the end of the day.  This occurs when caloric output is GREATER than caloric intake.

Certified Strength and Conditioning Specialists (CSCS) use this information to write a specific exercise prescription that is right for you and your specified goals.