How the Body Produces Energy?

Hello everyone. Thank you for visiting my blog and welcome. If you are a returning to SSP then welcome back. In this blog, I am going to discuss the energy systems of the body. It is going to be a little in depth at times in order to have all this make sense. So with that said, let’s begin.

The three main ways that the body utilizes energy are through the Adenosine Triphosphate Phosphocreatine (ATP-PC) system, anaerobic metabolism (without oxygen) system, and the aerobic metabolism (with oxygen) system. The body does not operate one at a time, but fluctuates between them all depending on the demands placed on it.

Chemical reactions of the body (metabolism) happen in two forms. The first is called catabolism or the breaking down of nutrients into usable energy (glucose). The second is anabolism or the building up to create. This occurs when the body is repairing damaged, old or dead cells etc. Food is catabolized into essential nutrients for energy and maintenance. There are six nutrients which are divided into macronutrients and micronutrients. The macronutrients are carbohydrates, proteins, lipids (fats), and water. The micronutrients are vitamins and minerals. They work together to provide renewable energy and continual repair.  

ATP

A major source of energy comes from carbohydrates. Utilization of carbs for energy is the most efficient method of energy metabolism, and they are vital to the healthy function of the brain and nervous systems. Carbs are broken down into glucose, fructose, and galactose. Glucose is the form of sugar we need to create a power house molecule called adenosine triphosphate (ATP is a high energy molecule that stores energy in the form of chemical bonds and supports muscle contractions by changing the chemical energy into mechanical energy during exercise). The liver uses glycogen phosphorylase to convert fructose and galactose into glucose. The glucose can then be used immediately for energy or stored in the muscles and liver as glycogen to be used later (like filling up the fuel tank in your car).

The Glycolytic (Anaerobic) system

The glycolytic system involves the anaerobic breakdown of carbohydrates to produce energy (glucose/glycogen). This process does not breakdown fats and proteins. The substrate (glucose or glycogen) must come from the blood or muscle stores.

The metabolizing of one glucose molecule yields two ATP’s (the energy molecule) without the presence of oxygen. Glycogen yields three ATP’s when metabolized. The ATP is catalyzed by the enzyme ATP-ase to create adenosine coupled with two phosphates (ADP) plus one inorganic phosphate (Pi) and 7 Kcals of energy. It is this release of energy that provides work potential. ATP is stored in the muscles for immediate use; however, it is stored in very small amounts. This limits the work potential of ATP to less than ten second and requires the body to produce a greater number of ATP’s to continue working. It’s like driving your car with the fuel light on. You are moving now, but if you don’t refuel soon you’re going to come to a halt.

Kinase is used to change ADP back to ATP

Enter creatine phosphate (PC) to save the day (I don’t think it wears red and blue tights though). ADP is metabolized into ATP with the use of the enzyme kinase. When PC is in the presence of ADP, kinase is used to bind them together creating a usable ATP molecule.  The creatine phosphate cycle is the quickest process to produce usable energy, but the yield is low. The PC system provides about 10 to 30 seconds of energy and is the primary energy system for high intensity short duration activity like power/strength training or sprinting. The PC system also provides energy at the beginning of all stages and types of exercise. It’s the “first gear” of energy production.  Fatigue is associated with a depletion of PC.

Anaerobic metabolism will provide energy longer than the ATP-PC system alone, but it is limited to about 30 seconds to 2 minutes and is the energy system used the most.  Lactic acid is the byproduct of anaerobic metabolism. We will not discuss the role of lactic acid in energy production at this time.

Oxidative (Aerobic) system

The oxidative system uses oxygen to metabolize carbohydrates and other carbon containing structures (fats and Proteins). This process is very slow but can yield 36-38 ATP’s per cycle. The oxidative system is the primary energy producer in endurance related exercise. Because the oxygen is used to produce energy, there is virtually no limit to the duration of energy production at lower intensity exercise.

One final note, the intensity of the exercise plays a large role in determining the primary energy system. Understanding how your body produces energy will aid you in reaching your next level of performance. This was down and dirty super abbreviated crash course in bioenergetics.  In the future, I may refer to different energy systems being used during exercise, and I hope this helps you follow along.

-Reuben

References

Van, De Graaff, Kent., R. Rhees, Sidney Palmer, R. Ward. Rhees, and Sidney L. Palmer. "Metabolism, Nutrition, and Temperature Regulation." Schaum's Outline of Human Anatomy and Physiology, Third Edition. N.p.: McGraw-Hill Companies, The, 2009. 337-46. Print.

"Exercise Metabolism and Bioenergetics." Nasm Essentials of Personal Fitness Training. [S.l.]: National Academy of Sports Medicine, 2014. 63-74. Print.

"Exercise Physiology." ACSM's Resources for the Personal Trainer. Philadelphia, PA: Lippincott Williams & Wilkins, 2009. 135-39. Print.

Chandler, T. Jeff., and Lee E. Brown. Conditioning for Strength and Human Performance. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins Health, 2013. 3-19. Print.