crossfit athletes training using different energy systems
Source: CrossFit Inc

Understanding The Effects of Training Different Energy Systems in Crossfit

Crossfit is a high intensity sport that trains our bodies in many different ways. Understanding how these energy systems work will help you to become a better athlete and improve your training and performances.

When we talk about energy systems, we basically mean the systems in our body that supply us with energy during a workout. ATP (adenosine triphosphate) is a molecule that contains a high amount of energy, and it’s the primary source used by the muscles for muscle contraction.


  1. ATP-PC
  2. Glycolytic system
  3. Oxidative system

Every energy system during exercising is active, but one is always predominant. The duration and the intensity of the workout are going to determine that.


For example, let’s take the first event in this year Crossfit games. It was a 7k trail run. The time needed to finish this event as we can see starts from 36 minutes and goes above. The body has to provide energy for 36 minutes and more. This is purely an aerobic event. The aerobic system in comparison to other systems can create the highest number of ATPs from single glucose molecule, but it requires a longer period of time to do so.

crossfit games 2016 sam briggs trail run energy systems

Sam Briggs during the 7km Trail Run

© CrossFit Inc


On the other hand, the second event, the Deadlift ladder, required the ability to generate high amounts of force. The athletes had to lift a heavy barbell, and the rest intervals between the lifts were very short, only 30 seconds. The ATP-PC system (which is the main energy supplier for exercises lasting from 0-10 sec) is working on replenishing the ATP broken down during the lifts. So, the anaerobic energy systems are very important, because they have the ability to provide us with higher amounts in short periods of time.

crossfit games energy systems

Lucas Parker mans up and Deadlifts!

© CrossFit Inc


Training different energy systems creates all-round athletes. Like we said, during a Crossfit workout you usually have to rely on more than just one energy system.

Training different energy systems provokes your body to react differently to the training. Those workouts when the energy supplied comes from the ATP-PC and glycolytic systems burn more calories during and after the workouts. Even though fat is burned during low intensity workouts, the total energy expenditure during those high-intensity interval trainings is greater, thus the total amount of fat burned is also greater. Studies have shown that the RMR (resting metabolic rate) stays elevated by 15% after the workout is done.

Training the anaerobic energy systems in Crossfit will improve your bodies’ ability to regulate aerobic, anaerobic and ATP-PC enzymes. You’ll be able to work longer at higher levels, burn and generate energy more efficiently.

barbell complexes from male crossfit athelete

barbell complexes improve strength and technique

© Stevie D Photography


The Crossfit athletes as we can see are big, strong, powerful and lean. This is a result of their training. The fast-twitch muscle fibres are recruited heavily during high-intensity workouts. These muscle fibers have greater CSA (cross-sectional area), leading to greater muscle size.


On the other hand, for longer, high-volume, low-intensity workouts, the body is recruiting more slowtwitch muscle fibres because they have greater endurance ability. During those types of workouts the muscles are supplied with energy through fat oxidation from the aerobic energy system. This allows the athletes to work for a prolonged period of time. Training different energy systems may be the reason behind such impressive aesthetics as well as athletic performance.


Working on the oxidative energy system is very important as well. The effects from those workouts include:

  • improved aerobic capacity
  • increased work durability
  • better ability to recover
  • increased number of mitochondria’s
  • increased number of aerobic enzymes
  • more oxygen and nutrients available to the tissues

You would think that these abilities will serve you well only for high volume, pure oxidative workouts/events, but you’d wrong. Recent studies are showing that the aerobic system is not completely shut down during anaerobic events. The recovery period after an activity is purely aerobic.

Crossfit WODs can be very challenging and taxing for every energy system.

Working on different energy systems like we have discussed has many effects on your body. But, let’s not fool ourselves. For the real benefits to be achieved from training them, you must pay attention to your nutrition as well. These things always go together. Always fuel your body properly at all times and make sure that you have the energy to perform each WOD to the best of your ability, and the nutrition to recover as effectively as possible afterwards.