The terms aerobic and anaerobic exercise literally mean exercise “with” and “without” Oxygen.  Our muscles contain both Fat and Carbohydrate (sugar) as sources of energy.  As we breathe we acquire Oxygen which is used in a chemical reaction with either Carbohydrate or Fat to produce energy.  Carbohydrate is the easiest form of energy to use and is the primary source of quick energy for most of our daily activities. 

During exercise Carbohydrate is first is converted to Lactic Acid as it is broken down to produce energy.   If there is plenty of Oxygen (Aerobic Exercise) this Lactic Acid is further broken down into more energy.  If there is not enough Oxygen (Anaerobic Exercise) then the Lactic Acid can not be broken down and it builds up in our muscles.  As the Lactic Acid concentration increases our muscles they start to burn they lose efficiency and we experience fatigue.    

If we engage in lower intensity exercise (Aerobic Exercise) long enough we eventually start to “run out” of Carbohydrate as fuel and our muscles then turn to the slower burning Fat as energy.  For most people it takes about 20-30 minutes of low intensity exercise before they “use up” their Carbohydrate and start using their Fat as energy. 

Therefore, during prolonged exercise we need a good combination of both Carbohydrate and Fat for energy.  We need the Carbohydrate for immediate and quick energy at the beginning of exercise and we need Fat as a sustainable source of energy once our Carbohydrate supplies run low. 

Now let’s put this all together in the example of a typical Tae Kwon Do class.  At the beginning we are doing jumping jacks and stretches at a low intensity.  We are breathing easily (Aerobic Exercise) and we are primarily using Carbohydrate in our muscles for this work.  Since there is plenty of Oxygen (Aerobic Exercise) we don’t build up Lactic Acid. 

Let’s say after we are warmed up we are challenged by a brief session of more intense activity (a sparring match maybe).  We are working hard and out of breath.  We still have Carbohydrate left in our muscles but we don’t have enough Oxygen to completely break down the molecule so we start to build up Lactic Acid (Anaerobic Exercise) therefore we start to fatigue.  When our match is over our breathing slows we catch up with our Oxygen needs and the Lactic Acid is cleared from our muscles (back to Aerobic Exercise). 

As the class progresses we eventually “run out” of available Carbohydrate and we begin using Fat as energy.  Fat burns slower so we start to lose our source of “quick energy” and Fat is very Oxygen dependant so we fatigue more easily but if our intensity is low we can be sustained on Fat for quite some time.  For most people if the exercise intensity is low enough we can be sustained on Fat for 2-3 hours.

Therefore the best exercise to burn Fat is a long session of low intensity (Aerobic) exercise.  So as you are warming up for your next Tae Kwon Do class,  remember that if you are working hard during the entire class the first 30 minutes is spent exhausting your Carbohydrate supply and the last 30 minutes is when you can best burn your excess Fat.

 Wade Weatherington, MD, FAAP         

Black belt promotions are only made twice a year.  In addition to promotions, students that have achieved the rank of black belt and are seeking to advance to higher ranks are required to credit test.  The students that were awarded a new black belt degree or credit tested are listed in the following tables.

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