Welcome to part 2 of a 3-part series on WHAT we train. We’ll be exploring skill development, conditioning, and strength building in this series. If you understand WHAT each component is, and HOW it affects our training, you’ll understand more of the WHY behind our workouts. While each component affects and intersects with the other two, for the purposes of understanding, it’s helpful to break each one out individually. Enjoy!

What We Train: Part 2 – Conditioning

Conditioning – in the context of CrossFit, conditioning is short for metabolic conditioning, which is also referred to as “metcon.” What is it? It’s training to increase your body’s ability to transfer energy from storage to a usable form that can be burned to support activity. All our cells burn Adenosine Triphosphate, or ATP, to function; ATP is our usable energy form. Our body has 3 different fuel sources that can be converted into ATP, each of which requires a different process. These processes are referred to as “energy systems,” and conditioning allows us to improve them. All 3 systems are always working simultaneously, but we can emphasize one over the others by changing the movements, rep schemes/loads, and time domains of our workouts. A balanced program should train all 3 systems. Let’s look at each:

Phosphagen (ATP-PC) System

In this energy system, our bodies break down a fuel source called phosphocreatine (PC), which is stored in our skeletal muscles, to create ATP. The body completes this process without using oxygen, so this system is anaerobic. PC is the most readily available fuel source, which is why it is processed first. Unfortunately, our PC stores are very small and can be depleted in as little as 10 seconds. If our PC stores are full (creatine supplementation can help here) and our phosphagen systems are well developed, we can drag this out to maybe 20 seconds.

The phosphagen system is also very inefficient – to completely recover from, it takes about 2 minutes. However, we can partially recover in as little as 30 seconds. By manipulating rest periods, we can greatly change the intent and outcome of a workout. Consider the following:

In the first variation, we are resting to complete recovery. As such, we would hope to see a consistent score across the board. In the second, we get incomplete rest. So, we expect a decline in power output, and therefore the calories earned each round.

Why choose one over the other? Each has a different goal. In the first, we’re SOLELY training the phosphagen system. In the second, as we deplete your PC stores, the secondary fuel source for your body comes into play. Which brings us to:

Glycolytic System

In this energy system, our bodies break down glycogen to create ATP. Glycogen is the stored form of glucose (a carbohydrate), and it’s found in our livers and skeletal muscles. As with PC, the conversion of glycogen to ATP does not require oxygen, which means that it too is anaerobic. And, as with PC, it runs out quickly. This system is dominant in exercise lasting 20 seconds to 2 minutes. If your glycolytic system is well conditioned, you might be able to extend its duration to 3 minutes. Complete recovery for this system varies, but usually takes about 6 times the work interval. So, for complete recovery from a 1-minute all-out sprint, you’d need 6 minutes.

Why do we care about this system? This is where most of the “high intensity” piece of CrossFit comes into play. Doing “Fran” unbroken heavily taxes this system, which is why you feel like complete crap after. In other words, developing this system allows you to PUSH HARD. We train your ability to push by using incomplete rest intervals. For example:

In this workout, your rest is going to be slightly longer than your work. Your first couple rounds should be fine, but you’ll likely have a drop-off in time by the end. That feeling of “hitting a wall” that we all experience in workouts like this occurs when we’ve depleted our glycogen stores. At this point, it is physically impossible to “push through it,” no matter how mentally tough you might be. Your body physically cannot; you have no choice but to slow down. Why? Because at that point, your body resorts to burning its tertiary fuel source. Which brings us to:

Oxidative System

This is your aerobic system, and it converts first carbohydrates, and then fat substrates into ATP in the presence of oxygen. Because oxygen is required, this process takes longer than those of the other 2 systems, which is why it kicks in last. It operates in activity lasting between 2 minutes and 3 hours. No matter how “high intensity” we claim a workout is, if it’s longer than 2-3 minutes of work with no rest periods, it’s going to be dominated by the oxidative system.

We train this system because it has  A TON of carryover to the high intensity side of things. If our oxidative system is well developed, we recover faster from our workouts. Furthermore, a well-developed oxidative system is associated with longer life (if you’ve ever heard that cardio is necessary for longevity, here you go.) Finally, when we perform longer workouts with the explosive, high intensity movements that we all know and love in them, we frequently need to break. Assuming the movements are technically simple, or that you’re proficient if they’re complex, a well-developed oxidative system will help you shorten your rest time between sets.

Mixed Modality

We just touched on the oxidative system helping you keep your rest periods short in a metcon. Depending on the movement, rep scheme, and weight you’re using, which system you tap into to execute that particular movement will vary. In a metcon with near max weight, you’re going to need longer rest periods so you can tap into your phosphagen system. If it’s lighter weight and you’re doing long-ish sets, you’re tapping into the glycolytic. All the while, depending on the workout duration, your oxidative system is running to help you recover. It is this interplay and overlap of energy systems that really makes CrossFit unique. While we can and do isolate each system to train individually, we can also train them simultaneously.

At the end of the day, if you want fast workout times, you need to develop all 3 systems. While different movements spike our heart rates differently, and we can mitigate some of these effects through technical proficiency and a strength base, we need to be able to push hard and then recover quickly. We also need to be able to pace at lower outputs for longer. By tackling different workouts and ensuring that we train individual systems as well as mixed modality, we’ll get there. Thanks for reading.