My objective with this topic is to raise the level of awareness about metabolic fuel systems (energy sources) used during exercise.  How can this information benefit you?  It’s important to know which fuel system to tax to better prepare for a particular sport or activity or to burn fat more efficiently.  Bear with me; this material is complicated and may require rereading this piece several times before you grasp the information.  The first of this two part series will explain the actual fuel systems.  They are the phosphagen system, glycolysis (fast and slow) and the oxidative system.  The phosphagen system supplies the body with the energy needed for short-term, high intensity activity and lasts only a few seconds (sprints or heavy resistance training).  Glycolysis is the breakdown of carbohydrates and has two stages, fast and slow.  Fast glycolysis creates the byproduct we all know and love called lactic acid.  It occurs when the intensity is too high and minimal oxygen is available.  Slow glycolysis occurs when there is sufficient oxygen present and leads into the oxidative system.  Both stages of glycolysis occur between 30 seconds and 3 minutes upon initiation of exercise.  The oxidative system can burn carbohydrates, fats or protein in the presence of oxygen to “fire-up” the Krebs cycle (TCA).  You can think of the Krebs cycle as this big machine that gobbles up amino acids, fatty acids and carbohydrate byproducts and spits out usable energy.  As carbohydrate sources are exhausted, the ratio of fat utilized increases in the oxidative system.  It’s important to note that all the fuel systems are active at a given time, but the level of involvement depends on the intensity of the exercise.  Next month I’ll further discuss the application of taxing particular fuel systems to better improve your activities.

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