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A Review of the Body's Energy Systems for Fitness and Athletics

I've been talking a lot lately about using the right form of energy system work (cardio) to get in peak condition for your chosen exercise activity. For example, one of the dumbest things I see in sports training is football coaches sending their linemen on 1-3 mile runs, and timing them! As far as their sport conditioning goes, that's pointless to the point of counterproductive. Since I've been harping on it I thought I'd give a quick overview of the body's four energy systems, the fuels used, and give an example.

The Creatine-Phosphate System (C-P System): The Creatine-Phosphate System, sometimes called the Phosphagen System is the body's fastest form of energy. It provides energy for extremely intense, short-term activities like heavy resistance training and sprinting that last around 10 seconds or less.

The C-P system utilizes stored creatine phosphate in the muscle to regenerate ATP (the actual energy of the body). Since only a small amount of creatine phosphate can be stored by the muscle this is a fast but very limited system. The body regenerates creatine phosphate but the process takes time. This is why an athlete can't maintain their top speed for any more than a few seconds.

Fast, heavy lifting, short sprints, and any short stressful activity under 6 seconds or so are the best methods of training the C-P system.

Fast Glycolysis: Glycolysis is the process by which the body breaks down carbohydrate (sugar) for energy. This can be done in the muscle by breaking the carbohydrate down into pyruvate or lactic acid. During the course of this conversion some ATP is regenerated and utilized for energy. Oxygen is not required for lactic acid to be created and so this process is sometimes called anaerobic glycolysis. Since the production of some ATP and lactic acid is a fairly fast process this system is used for short duration activity as well.

Fast glycolysis is utilized during longer strength training sets and high intensity activities lasting longer from 6 seconds to about two minutes. Mid-range sprints and fast strength movements can train this system. Most American football players utilize the C-P system and fast glycolysis to provide the energy they need during play.

Slow Glycolysis: When oxygen is available glycolysis operates a little differently. During slow glycolysis (sometimes called aerobic glycolysis) the end result of the breakdown of carbohydrate is some ATP and pyruvate as opposed to lactic acid. The pyruvate is then passed on to the Krebs Cycle (the body's main power plant) in the cell's mitochondria where it can be further broken down to create more energy. As such slow glycolysis is much more efficient than the C-P system or fast glycolysis in that it nets much more ATP per molecule of sugar used. However, it's a much slower system, trading speed for efficiency.

Slow glycolysis is trained with exercise lasting longer than two minutes but is still fairly intense. Short, fast runs and sets lasting longer than two minutes are the best ways to train slow glycolysis. The development of the fast and slow oxidative system is the most important for most fitness goals. Most athletic activities rely on a combination of the two and they are also among the most effective training protocols for body fat loss.

The Oxidative System: The oxidative system consists of slow glycolysis, covered above, and beta-oxidation. Beta-oxidation is the series of reactions by which free fatty acids are broken down in the presence of oxygen. This results in acetyl CoA and hydrogen atoms. The acetyl CoA is sent directly to the Krebs cycle and the hydrogen is sent to the electron transport chain to squeeze out a few more ATP. This is by far the most efficient energy system in net ATP created, but also the slowest.

Beta-oxidation is the energy system primarily used by the body to create energy while at rest or during very low intensity exercise like long, slow running, cycling, or walking. Most long distance runners have developed a very refined oxidative system.

With a solid understanding of how your body works it becomes much easier to develop an efficient and effective exercise training program. By identifying and targeting the right fitness qualities you'll cut down on your wasted time in the gym and increase your training results.

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Isaac Wilkins, M.Ed, CSCS, NSCA-CPT

Training athletes and driven individuals in Charleston, SC and beyond. Get strong, get fast, become the new you.

posted by zgrsx @ 5:35 PM