Introduction to Energy Systems Training

R3VIVE Fitness • December 7, 2023
Man lunging with barbell at a gym; another person works out in the background.

Have you ever noticed that some workouts have an EN label next to them? These labels refer to specific energy systems being trained that are based on our ability to deliver oxygen to our muscles and to best utilize it.

If you ever took a biology class, you might have learned about three traditional energy systems: ATP or phosphocreatine (anaerobic), glycolytic (anaerobic), and oxidative (aerobic). In training, each of these energy systems have different response times and need different amounts of time to recover from and to adapt to.

Members working on pull ups during functional fitness class.

ATP is a chemical compound that our muscles use to contract, i.e., perform work. We always have some ATP stored in our muscles ready to be used, but we can burn through that storage very quickly, in about 5-10 seconds. We use this energy system when we do heavy lifts or 10 second sprints.

Once we run out of ATP, we enter the glycolytic system . This is where we take the glycogen in our blood and use it to create more ATP in order to produce more muscle contractions (i.e., perform more work). We are typically able to utilize this system anywhere between 10 seconds to 3 minutes. The glycolytic energy system is used in most of our lifting and sprint style workouts. The final energy system is oxidative or aerobic . This is where we use oxygen to create more ATP. Since we are able to continuously bring more oxygen into our bodies, we can operate under this energy system for 3 min or longer.

A member working on rowing at a challenging pace.

What these traditional energy systems don’t tell you is that oxygen is the major component in creating ATP. When our muscles run low on oxygen, we lose the ability to generate more ATP and, consequently, the capacity to contract the muscle and perform work. Therefore, the new energy systems that we refer to in our programming are all about our ability to deliver oxygen to our muscles and to utilize it effectively.

These new energy systems, totaling seven, are categorized on a numerical scale (1-7). The training objectives range from enhancing our ability to deliver oxygen (i.e., bringing in more fuel, EN 1-3), to optimizing oxygen utilization within the muscle for increased ATP production (EN 6-7), and to maintaining homeostasis by delivering and utilizing oxygen at a balanced rate (EN 4-5).

Consider the analogy of charging a device. The more efficiently we charge it (delivery), the more energy the device can use without running out (utilization).

Over the next few weeks we will provide more examples of how each of these energy systems are utilized and how we use them during our functional fitness classes.

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