Have you ever stopped and wondered how your body produces energy? While the fuel we use to walk and run and lift weights may seem as if it’s coming from nowhere at all, in truth our body is relying on multiple complex systems to produce the energy we need to exercise, walk around, and survive.
As simple as it may seem, even flexing your index finger requires a little bit of energy, and without this energy, we wouldn’t get very far at all. So how exactly does our body go about producing the energy we require? We know that food is a primary source of fuel, but how do we turn the food we eat into usable energy that allows us to thrive?
If we were to break out a microscope and examine our body on a minuscule scale, we’d find that three primary energy systems within our body are working endlessly to carry out this mission. These include the anaerobic glycolysis energy system, the aerobic glycolysis energy system, and the phosphagen system. So what do each of these systems do? Let’s examine them in further detail below.
The Three Primary Energy Systems
The body produces power via three primary energy systems that are also referred to as metabolic pathways. The anaerobic glycolysis energy system does not require oxygen and uses the energy contained within glucose (simple sugars) to form adenosine triphosphate, or ATP for short. ATP is the organic chemical that drives the many processes in living cells because it is a form of energy and is found in all forms of life.
The aerobic glycolysis energy system, on the other hand, requires oxygen to burn fats and carbohydrates for energy but again produces ATP.
But the third and final system, referred to as the phosphagen system, creates creatine phosphate to convert into ATP. Of the three systems that exist, this is the fastest energy system within our body — the energy it produces is immediately available for use.
Today we’re going to focus on that final energy system, the phosphagen system, in more detail. What occurs in the phosphagen system that provides us with energy? And why is this system so important among the three that exist? To find out, let’s take a closer look at the many intricacies of the phosphagen system.
What Is the Phosphagen System?
Imagine for a moment that you’re at the starting line for the 100 meter dash. You crouch to the ground and secure your feet against the blocks. From the corner of your eye, you can see the official raise the starting gun. Seconds turn into minutes, and your heart is beating out of your chest as you prepare for the competition that lies ahead. On your marks, get set, GO! The starting gun fires.
You burst from the blocks with explosive power due to your well-established reaction time, catapulting forward as you race down the track. Other sprinters are running at your side using every ounce of strength to overtake you, but slowly you break away from the pack with each stride forward. In a matter of seconds, you’ve crossed the finish line, out of breath and completely drained. The race is over, and you’ve won.
How did it all happen so fast? In the blink of an eye your body went from a standstill crouched position to throttling forward at top speed, careening down the track as countless muscle contractions and high-intensity energy production took hold. Believe it or not, this was only possible because of one crucial energy system: the phosphagen system.
During short-term, intense activities, the body relies on immediate sources of energy to generate large amounts of power within your muscles. To do so, your body requires an immediate source of ATP — that organic chemical we mentioned earlier whose role is to fuel muscle cells during everyday movements. So where exactly does this immediate ATP energy come from?
The energy we use in the phosphagen system comes from creatine phosphate, also referred to as phosphocreatine or PCr for short. Our body synthesizes creatine phosphate in one of two ways: either from the ingestion of meat, which contains creatine, or from the liver, kidneys, and pancreas, which produce creatine.
Once creatine is absorbed by the body, it’s stored in the skeletal muscles until we need it for energy. To produce creatine phosphate from creatine, our cells use a complex enzyme called creatine kinase that transfers a phosphate group to creatine, thus creating creatine phosphate.
After the body has synthesized creatine phosphate, it can then transfer that phosphate group to adenosine diphosphate, or ADP. ADP differs from ATP because it lacks one phosphate molecule. But this is a crucial point because ADP can’t be used for energy — only ATP can.
After creatine phosphate transfers a phosphate to ADP, it is converted into ATP and is then ready to be used as energy. Thus the phosphagen system is working in natural order, ready to meet our energy needs. But what makes this system so important? Let’s delve into the answer below.
The Importance of the Phosphagen System
Now that we have a basic understanding of how the phosphagen system operates, it’s time to explain why this system is so important.
Take a moment and think back to that scene we painted above where you found yourself sprinting down the track at lightning speed. If we were to classify that form of exercise as either a short-duration exercise or long-duration exercise, chances are you could guess that it would be rather short. It likely takes a mere 15 seconds to travel 100 meters, so it’s very different from the longer periods of time it would take to run a long distance like a mile.
Now think back to the three energy systems we described in detail when we introduced the phosphagen system. Alongside it were the other two energy systems that included anaerobic glycolysis and aerobic glycolysis.
Our body is a rather smart machine that determines when we should use each of these systems. And choosing which one we should use depends on the exercise at hand.
For instance, anaerobic glycolysis is perfectly suited to provide us with energy when we need a large burst of energy that may last anywhere from 30 seconds to 3 minutes at a time. Yet because this system doesn’t use oxygen, lactic acid (one of the many by-products of activity) can build up in our muscles and make them sore, causing us to fatigue and tire.
Aerobic glycolysis, on the other hand, is a system that uses oxygen and is perfectly suited for low-intensity activities that require sustained energy production over longer periods of time, such as running long distances or hiking up the side of a mountain. The energy system our body decides to use is based not only on the exercise, but the exercise intensity as well.
The phosphagen system is so important among these three systems because it is the initial means of energy production that comes before anaerobic glycolysis. It is reserved for high-intensity activities like sprinting or strength training because the ATP it produces is readily available and quickly produced by the body.
Though the phosphagen system will use ATP quickly, ATP production will still remain high when we utilize this system as a means of working muscles via anaerobic exercise.
It should be noted, however, that all of these systems contribute to the overall amount of ATP levels we have during physical activity. Though we may be able to manipulate and biohack our body’s means of using energy, all three systems are still used just the same.
These systems, though different in how they provide energy, do not work independently of one another. Instead, they dominate at different times during a workout depending on the intensity and duration.
Understanding the Three Metabolic Pathways
While the phosphagen system is considered an immediate source of energy for our body, in truth we rely upon all three metabolic pathways to produce the necessary ATP molecules that fuel our everyday needs.
From sprinting to walking to simply getting out of bed, a constant stream of ATP is forever pushing us forward. The next time you line up for a sprint or prepare to deadlift a serious set of weights, remember the importance of the phosphagen system and the role it plays in your daily endeavors.