The Phosphagen Energy System and Creatine Supplementation

As part of our Biohacking Masterclass Series, we will explore a number of different techniques and practices to improve your daily performance. This series will range from obvious subjects like exercise and nutrition to fringe subjects like breathing techniques and sleep hygiene. Consult your physician before implementing any of these topics. We are not your physician. Note: This post may contain affiliate links to the products we use. 


In short-duration high intensity exercises like sprints or resistance training, one energy system reigns supreme. In fact, it is active at the beginning of any exercise to some extent. Optimizing this energy system in your training will help you become a faster and stronger athlete. Specifically, adaptations in your phosphagen energy system can enable athletic transformation.

In order to understand how you can perform more short duration high-intensity work, we’ve broken down the basics of the phosphagen energy system. 

Muscle contractions (and many other bodily processes) require energy in the form of ATP (adenosine triphosphate, meaning 3 phosphate groups attached). Because so many basic processes require a stockpile of ATP (i.e. breathing, digestion, etc), muscle cells only get a certain allocation. When muscular ATP is broken apart to supply energy for contractions, a molecule called ADP (adenosine diphosphate, meaning 2 phosphate groups attached) is produced. After muscle contractions consume stored energy, muscles need to produce more ATP from the new ADP. 

The body’s first response to produce more of this energy is with a different molecule called creatine phosphate (or phosphocreatine). An enzyme called creatine kinase “takes” the phosphate off of creatine phosphate and adds it to ADP to produce a fresh ATP molecule that can supply energy for more contractions. When this step happens over and over again, creatine phosphate supplies enough energy for short-term anaerobic exercise. 

But what happens to the creatine part of creatine phosphate after the enzyme “steals” the phosphate group? 

During recovery/rest periods, a phosphate group is added to the creatine molecule to restore the original creatine phosphate, which can then be used to produce more ATP. 

This cycle is repeated throughout exercise, and fatigue during short-duration high-intensity anaerobic training is believed to be partially due to a decrease in available creatine phosphate. Creatine phosphate stores are thought to be moderately depleted during the 5-30 second window and nearly completely depleted after training to exhaustion (such as AMRAP-style exercise). 

How long does it take to replenish creatine phosphate stores? 

Repletion of the complete creatine phosphate stores is believed to take between 5-8 minutes. Additionally, the total amount of creatine phosphate stored in muscles can be adapted with training and supplementation. Type II fast-twitch muscle fibers inherently contain higher amounts of CP than type I slow-twitch fibers and may be able to restore ATP levels at a faster rate. 

Further, programming your training for hypertrophy in type II fast-twitch muscle fibers can increase resting levels of CP. We’ve detailed a proven method for training fast-twitch strength and hypertrophy gains here (part 1) and here (part 2)

But what about supplementation? 

Supplementing with creatine can increase the pool of molecules to which a new phosphate group can be added. By increasing the back-end components of CP, one can increase the total number of available creatine phosphate molecules during recovery periods. 

Therefore, creatine supplementation improves the resting levels of CP and enables a greater duration and potentially greater performance during high-intensity anaerobic exercise. If you want to be a faster, stronger, more competitive athlete, creatine is one of the safest and most proven supplements available. 

If you’re looking for more cerebral benefits as well, creatine is considered a nootropic. Nootropics are compounds that can potentially improve cognitive function and overall mental performance.