A review of the body’s energy systems for fitness and athletics

I’ve been talking a lot lately about using the correct form of energy system work (cardio) to be in optimal 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 your sports conditioning goes, that makes no sense to the point of being counterproductive. Since I’ve been harping on this, 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 (CP system): The creatine-phosphate system, sometimes called the phosphate system, is the body’s fastest form of energy. Provides energy for extremely intense short-term activities, such as intense resistance training and sprinting, that last around 10 seconds or less.

The CP system uses the creatine phosphate stored in the muscle to regenerate ATP (the body’s real energy). Since muscle can only store a small amount of creatine phosphate, this is a fast but very limited system. The body regenerates creatine phosphate but the process takes time. This is the reason why an athlete cannot maintain his top speed for more than a few seconds.

Fast heavy lifting, short sprints, and any short, stressful activity under 6 seconds are the best methods to train the CP system.

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

Fast Glycolysis is used during longer strength training bouts and high-intensity activities lasting more than 6 seconds to about two minutes. Mid-range sprints and fast power moves can train this system. Most football players use the CP system and fast glycolysis to provide the energy they need during the game.

Slow glycolysis: When oxygen is available, glycolysis works a little differently. During slow glycolysis (sometimes called aerobic glycolysis), the end result of carbohydrate breakdown is some ATP and pyruvate instead of 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 CP system or fast glycolysis, generating much more ATP per molecule of sugar used. However, it is a much slower system, trading speed for efficiency.

Slow glycolysis is trained with exercise that lasts more than two minutes, but is still quite intense. Short, fast runs and sets that last more 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 sports activities are based on a combination of the two and they are also among the most effective training protocols for losing body fat.

The oxidative system: The oxidative system consists of slow, covered glycolysis 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 extract a little 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 used primarily by the body to create energy while at rest or during very low-intensity exercise, such as long, slow runs, cycling, or walking. Most long-distance runners have developed a highly 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 physical qualities, you’ll reduce time lost in the gym and increase your training results.

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