In part 1 we introduced the idea of energy systems and explained how the body produces energy to meet the demands of a particular environment.  Energy management is critical for more than just sports performance, you can only get out what you put in and your body prioritises survival over both health and fitness. If you're not eating enough nutrient dense foods for survival, there is zero chance your immune system is going to stay healthy and give you the energy to train. 

In this weeks post, we are going to take a closer look at the Alactic Phosphocreatine energy system (ATP-PC) and the activities that depend on it. From a biological standpoint, the ATP-PC system plays the most significant role in the “fight or flight” phenomenon (driven by the sympathetic nervous system state). This ATP-PC energy system provides short, explosive bursts of power that are most activated by a survival instinct (running away from the tiger or standing to fight the tiger). In a life and death situation, you want to be able to activate the most potent energy system you have.  


The ATP-PC is anaerobic because it doesn't require oxygen to function. The ATP-PC system is responsible for providing energy to the highest threshold muscle fibres that are capable of producing the greatest levels of force. It makes sense that bigger stronger muscles generate more power due to their storage capacity for phosphocreatine. The ATP-PC system is the most genetic and the least adaptable of the energy systems.

The high power output of the ATP-PC system cannot be maintained for long periods of time,  typically only lasts for 10-15seconds. This high energy output places high levels of acute stress on the nervous system and quickly depletes local Adenosine Triphosphate (ATP) stores in the muscles, therefore long rest periods are required between repeated efforts.   The nervous system takes far longer to recover than the muscular system, and this is why you see many Olympic weightlifters taking 6-10mintites rest between their heavy sets in training.

All muscles have small levels of ATP stored within them that can be accessed immediately because the ATP-PC system has the fewest chemical steps of the three energy systems. We are talking instant power baby! The local store of the high power energy compound phosphocreatine can supply the energy needs of a working muscle at very high rates, but only for a concise period (think Olympic lifting, throwing sports and sprinting).

The total energy output and duration of energy output are unique to each athlete because it depends on the local stores of ATP, phosphocreatine and the specific enzymes that are used in the chemical steps to regenerate ATP. Because only small levels of ATP are stored locally in the muscles, and the body uses it up in the first few seconds of high-intensity work, ATP must be restored for repeatable efforts.  ATP is replenished by using phosphocreatine to convert adenosine diphosphate (ADP) into ATP in the mitochondria of cells within the muscle tissue.  ATP is therefore produced from glucose (carbohydrates) through the glycolytic pathway.  

It's important to be aware that while the ATP-PC system may be prominent during high power activities, both the aerobic and the anaerobic lactic system are contributing to the energy production.  One of the reasons why the ATP-PC energy system can produce such high levels of energy is due to the support it gets from the other energy system.  This is especially true if multiple efforts are required because both the aerobic and anaerobic lactic systems are used to recharge the ATP stores within the muscles.  The stronger the aerobic system, the faster an athlete can recover between ATP-PC intervals, this is why sprinters often train the aerobic energy system in the offseason.

The Biology of Glycolysis:

To make ATP, phosphocreatine transfers a phosphate molecule to ADP. The newly-formed ATP is now available to be used for muscle contraction. The leftover portion of phosphocreatine is creatine, which is processed by the liver into creatinine and eliminated through the kidneys and urine. The body doesn't recycle this creatine into phosphocreatine.

Training the ATP-PC energy system can be achieved by using short (3-10sec) high power demand physical activities followed by 1-3+ minutes of rest.  The very high power demands require an extended period of rest to allow for the system to recharge.

Note: while the ATP-PC system does not produce lactate, the anaerobic lactic system is at work at the same time so lactate is produced.  The use of the ATP-PC system lead to the fastest rate of fatigue, it should be used wisely.

For sports and exercises that require explosive and powerful muscle contraction, there is a lot of interest in maximising phosphocreatine in the muscles to boost performance. If you have more phosphocreatine in a muscle, you are able to endure a longer period of intense muscle contraction before the muscle is fatigued and loses power. To increase the levels of ATP-PC fitness one must increase the size and contractile ability of these muscle fibres.

What foods contain Creatine?

Creatine is most abundant in red meat, pork, poultry, and fish. There is much less in dairy, eggs, and shellfish. Creatine is mostly stored in muscle meat; organ meats such as liver, heart, and kidney have very little.  Wild game meat and organic grass-fed meat contains high levels of creatine than grain-fed meat, the quality of your protein is important and athletes should invest in eating good sources of protein before spending money of protein supplements.

Can supplement with Creatine help performance?

Creatine monohydrate will help you regenerate ATP faster during high-intensity exercise, allowing you to maintain a higher power output for longer. The recommended daily intake is around 5g and its best to take post training to replenish stores. Studies have also shown that taking creatine with carbohydrates increases the uptake in the muscle tissue [1,2,3]. For this reason, low carb diets may not be the best choice for athletes who want to maximize their explosive muscle power. If you would like to know more about supplementing with creatine I recommend you check out the

There are plenty of studies that support taking creatine to improve sports performance but this is not the topic of today's post, we are simply talking about ATP-PC energy management. Creatine has more reliable effects on muscle gain than any other common supplement. It’s been used as a novel treatment for addressing depression in some preliminary trials. Side effects are few and far between.



Energy System: Alactic Phosphocreatine
Power Output:  Most powerful
Duration of Activity: 10-15seconds
Time to Recovery:  Slowest of the three energy systems.  Training methods for ATP-PC fitness must be short 3-10seconds, with long rest periods, 1-3+minutes or more
Prefered Source of Energy: Anaerobic (without oxygen), Phosphocreatine, Glucose (carbohydrates)
Adaptability: Least adaptable
Sports: Explosive Power Sports like Olympic Lifting, Powerlifting, Sprinting, Throwing., etc...  It's worth noting that most team sports are aerobic-alactic in nature


  1. Role of submaximal exercise in promoting creatine and glycogen accumulation in human skeletal muscle, Robinson TM, et al, 1999

  2. Muscle glycogen super compensation is enhanced by prior creatine supplementation, Nelson AG, et al, 2001

  3. The Complete Guide to Sports Nutrition: 8th edition, Anita Bean, 2017