Basic Understanding of the Body's Energy Systems

For human movement to be possible, energy must be readily available. In order for humans to get energy, food must be ingested so that it can be converted to adenosine triphosphate (ATP) through metabolic processes beginning with digestion. In other words, as food is digested into useable forms (carbohydrates into glucose, proteins to amino acids…), the human body uses them to either: supply energy for other metabolic processes, supply energy for movement, supply other essential vitamins and minerals, or build/repair various cells and tissues. Although it makes sense, the science that is Bioenergetics is as complicated as it is intriguing. A thorough understanding of how it affects the human body can greatly influence how one trains for general fitness and/or athletic performance.

Earlier, I mentioned that food is converted into ATP through metabolism. ATP is important as it is a key component for muscular activity and growth. Therefore, without ATP, movement would not be possible. ATP is stored in limited amounts within our muscles but daily activities(work, exercise, play, chores…etc) require the need for constant ATP production to keep up with the demand.

ATP production occurs at the cellular level through either aerobic(with oxygen) or anaerobic(without oxygen) metabolism. Depending on the demand and duration of any physical activity, one of three energy systems takes the brunt of the workload. These energy systems are the: Phosphagen, Glycolytic, and Oxidative systems.

The Phosphagen system creates ATP anaerobically and is the primary source of energy for short-term high intensity exercises such as sprinting, jumping, running a single football play, performing a single acrobatic pass in gymnastics…etc. This system is active at the start of ALL exercise, regardless of intensity simply because ATP is readily available within the muscles.

The Glycolytic system utilizes glycolysis to create ATP aerobically or anaerobically. Glycolysis is a metabolic process that breaks down the carbohydrate stores either from: glycogen in the muscles or blood glucose. The Glycolitic system initially supplements the Phosphagen system with ATP before becoming the primary source of energy once high intensity activity lasts up to two minutes. Think the early parts of a boxing round, a rigorous volley in beach volleyball, or running 600m. A more thorough explanation of the Glycolitic system can be found on youTube by typing "Understanding the Glycolytic Energy System. (Sorry, I haven't quite figured out how to get the links to work here quite just yet.)

The Oxidative system is sort of unique as it is active when the body is at rest and during prolonged bouts of aerobic activity that last longer than 3 minutes(Jogging, lap swimming, cycling). When at rest, about 70% of ATP production is derived from fats while 30% from carbohydrates. Once aerobic activity begins, there is a shift in which carbohydrates are preferred more so than fats for ATP production, especially during high intensity aerobics. However, during moderate intensity aerobic exercise, the shift returns to fats for energy. This bit of information, at first, may seem to be counterintuitive for individuals who are working to lose weight in terms of fat mass. Yet, this is another factor that makes the oxidative system unique. Depending on the intensity, a person may be burning energy stores from an undesired source in relation to the overall goal. If you’re the type of person looking to lose fat mass, moderate intensity aerobic bouts need to be adhered to as part of your exercise program.

It’s important to know that at no time, no single energy system provides 100% of the energy supply. During exercise or other physical activity, the varying degrees of intensity require a constant shift from one system to the next. As ATP is depleted from one system or as exercise intensity/duration increases, the next system begins to supply ATP as needed. Therefore, we can compare the three energy systems as gears in an automobile. By switching energy systems, the body can EFFICIENTLY utilize its energy stores before completely running out.

A deeper understanding of these energy systems allows an individual to train smarter, not harder. Through quality coaching, training, and support; Injuries caused by overreaching or overtraining are better prevented. It should also influence nutrition and weight management. Yet, what I believe to be more important is that by realizing what energy system we focus on allows our bodies to better adapt to specific activities for enhanced performance.

References

Telfer, Andrew. "Understanding the Glycolytic Energy System." EAST Fitness Foundations, 22 November 2014. Online Video. 7 September 2016. <https://youtu.be/Xf0a-XWHmR4>.

Triplett, Travis N. "Bioenergetics." Coburn, Jared W. and Moh H. Malek. NSCA's Essentials of Personal Training. 2nd. National Strength and Conditioning Association, 2012. Kindle Edition.

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