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.

Apex Training Cycle

By Derek Saffold • December 26, 2025
Hey R3VIVE Athletes, The Apex training cycle, going from January 5th to April 3rd, is our next training cycle! This will be the firt training cycle of the new year! this is a chance to refocus and get in some good work to help you reach your goals! lets all work together to crush this training cycle! Functional Fitness: The Apex Cycle is designed to make your year-long strength work truly functional, focusing on controlled, powerful movements, complexes under fatigue, and mandated touch-and-go reps to prepare you for mixed-modal workouts. Our strength culminates in the classic CrossFit Total and the "R3VIVE Other Total," while conditioning features a wide variety of time domains, movement volume builds (like wall balls, toes-to-bar, and burpees), and regular Friday retests of past workouts to track your progress and ensure you perform your absolute best. Build: Designed to bring together all your training from the past year and prepare you for your strongest performance yet. Our strength work will focus on controlled, powerful movements, building you up to test your limits with both the classic CrossFit Total and the "R3VIVE Other Total," which challenges your skill and strength balance. Expect a well-rounded program including unilateral strength, skill work, and core stability, with dedicated days for deadlifts, squats, gymnastics, and varied accessory work to keep you healthy and constantly progressing. For conditioning, we're tailoring the work to challenge you in new ways, featuring a wide variety of time domains and movements, and a specific volume build on common movements like wall balls, toes-to-bar, and burpees. Instead of a standard test/retest, we'll be performing regular retests of past workouts on Fridays, allowing you to easily track your progress and see how far you've come. Our weekly template balances intensity—with short, fast metcons on Mondays—with recovery, incorporating lower impact endurance work on Thursdays, and a strategic taper toward the end of the week to set you up for success on Friday! Partner workouts will wrap up your week every Saturday, bringing the whole community together.

Ultimus Training Cycle

By Derek Saffold • October 30, 2025
Hey R3VIVE Athletes, The Ultimus training cycle, going from November 10th to January 2nd, is our next training cycle! Functional Fitness will be launching into a blend of olympic lifts and diverse strength progressions. Including more intense conditioning and gymnastic strength and skill development. Functional Fitness: We're taking the solid foundations from all our Machine work (which we know you loved) in the Persist Cycle and launching into a blend of olympic lifts, foundational strength, and diverse strength formats. Prepare for tough but fun challenges, gymnastic strength and skill development, and an intensified focus that will push your limits and build your confidence further than you ever imagined! Build: This Build cycle is your blueprint for forging general strength with a rock-solid, consistent split. While we will have linear progressions of Front Squats, and Bench Press, we will also be embracing varied, dynamic strength orgressions. That will not only keep delivering results but also keep our strength fun. Our gymnastics focus will be on pure, raw strict strength, helping you build capacity with both external loads and the incredible power of your own bodyweight. Prepare to feel incredibly stable and powerful! Conditioning will focus on unleashing your engine, that we built in the Persist Cycle . We will Shift gears to a fastermore intense "for time" AMRAP and Chipper style workouts, moving beyond simple interval work and aerobic base building. These conditioning workouts will rotate dynamically throughout the week to maintain variety and deliver a fun and powerful exeriance. our cycle test, "Super Bario Bros.", is a chipper that will progressively challenge your kettlebell/dumbbell and gymnastics movements, demanding peak intensity and absolute confidence in your strength.

Persist Training Cycle.

By Derek Saffold • September 22, 2025
Hey R3VIVE Athletes, Our next programming cycle runs from September 15th to November 7th. It's an 8-week cycle that will continue to see strength progression carrying from what we did last cycle in Functional fitness. While Pump will begin working unilateral strength progressions. Functional Fitness: This cycle will continue our progression from the skill and lifts from last cycle, while trying to integrate them into more of our conditioning. We will do this by focusing on different portions of the lifts during our strength portion then performing smaller sets of gymnastic skills in our conditioning. You will also see conditioning that is purely focused on our aerobic capacity and working mainly on monostructural elements, such as running, rowing and biking. Build: This A-B week cycle is designed to build foundational strength through consistent progression, with a strong focus on Back Squats and Strict Presses, including variations for balanced weekly training. Conditioning will have some longer aerobic pieces and begin to include more skills like strict Toes-to-Bar, and Pull-ups from last cycle. See the chart below for details.
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