Applied Energy Systems

Have you ever wondered how your body produces energy to produce movement? In this post, I will cover the 3 basic energy systems the body utilizes to contribute to the formation of adenosine triphosphate (ATP), which is what the body uses for energy. The three basic systems are the following: ATP-PCr system, Anaerobic Glycolysis and Oxidative Phohsphorylative Pathway.
Let’s first examine the ATP-PCr system. This system along with anaerobic glycolysis is anaerobic in nature. This means that it doesn’t require oxygen to produce ATP. Anaerobic exercise consists of high intensity exercise lasting less than 2 minutes. The first 3 seconds of exercise uses up stored ATP. The ATP-PCr system only regenerates ATP for about 10 seconds after the onset of intense activity.
Exercises that utilize the ATP-PCr system would include 40 yard dash, weight training in a low rep range, short sprints, complexes, Olympic weight lifting , gymnastics etc. Basically any action, which requires you to produce muscular force in a short time will utilize the ATP-PCr system. This system will run out when your creatine phosphate (CP) levels deplete. This is the reason that creatine is such a highly used and studied supplement. Taking creatine will increase CP levels, resulting in improved strength and muscular size.
Once CP levels are too low, ATP is generated by anaerobic glycolysis. This system utilizes glucose (broken down carbohydrates) for energy. It is active during intense exercise from about 10 seconds until 120 seconds. Exercises that depend on this system include: 200 metre sprints, wrestling, soccer, hockey, and basketball. After 120 seconds, the system must slow down due to high levels of hydrogen ions, which brings us to our next energy system.
The aerobic energy system or oxidative phosphorylative pathway is the most efficient energy system. It produces more ATP then both anaerobic systems. However, it produces ATP at a slower rate than the anaerobic system, which is why it takes longer to start. I won’t go into detail about how it produces ATP, but check out Kreb’s cycle and the electron transport chain if you want more information.
The aerobic energy system can be fueled by glucose (broken down carbohydrates), amino acids (broken down protein) and fatty acids (from broken down triglycerides). Glucose, amino acids and fatty acids are all converted to Acetyl-CoA. Acetyl-CoA is the entry molecule into the Kreb’s cycle.
The aerobic system is utilized during longer, low-intensity exercise. Walking, jogging, cross-country skiing, long distance swimming are all examples of exercises that use the aerobic energy system. As mentioned above, fatty acids can be converted to Acetyl-CoA. This is why the ‘fat loss’ zone exists. It is true that training in this zone, which is around 70% max HR will result in fat loss. Just remember, there is more than one way to skin a cat. Intervals, circuits, complexes are just a few ways you can accelerate fat loss. So don’t get stuck on only aerobic training!

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