The Phosphagen System
TL; DR Version:
1) The phosphagen system produces immediate, but short lived, energy.
a. Example: Jumps, throws, sprints, high-intensity resistance training.
2) The phosphagen system functions in absence of oxygen.
a. It can sustain exercise for maximal effort bursts of approximately 10-seconds.
3) The phosphagen system uses creatine phosphate to resynthesize ADP into ATP.
4) It can require anywhere from 2-5+ minutes to fully recover after maximal effort exercise.
Our body responds to energy demands by mobilizing its available ATP stores. Once this happens, a feedback mechanism begins to register a depletion of ATP and an increase in ADP molecules (and to a lesser extent, adenosine monophosphate (AMP)). This triggers a series of events meant to begin recycling these ADP molecules back into ATP to provide sustained energy for the required tasks.
The first energy system to kick on is the phosphagen system. The phosphagen system is composed of a base level of ATP and a corresponding pool of molecules called creatine phosphate. This pool of creatine phosphate will engage in a one-step chemical reaction with the accumulating ADP molecules in order to resynthesize them back into ATP for repeated use.
This energy system is responsible for providing a short-term burst of energy for very rapid tasks or exercises. This energy is predominantly harnessed for exercises that don’t require oxygen; or more specifically, cannot wait for an oxygen based (aerobic) system to provide sustained energy. Examples of these exercises would be jumps, sprints, lifting weights for a high-intensity set, throws, or any number of similar exercises.
The available creatine phosphate donates their single phosphate group to the accumulating ADP molecules in a near-immediate reaction – buffering the amount of time the phosphagen system can remain active before requiring assistance from other energy producing systems. That said, this system is still extremely short lived. The base amount of available ATP (even when buffered by the creatine phosphate reaction) can still only provide energy for approximately 10 seconds of maximal exertion.
The experience of exercising within the phosphagen system is typically one that doesn’t really feel like anything. Exclusively harnessing the phosphagen system does not produce a burn (as we’ll explore in the glycolytic system) and this fact can help define our exercise parameters to correctly train specific energy systems for our goals.
While this system only gives “feedback” of its use once it has been fully exhausted (via the glycolytic system beginning to produce a feeling of burning within the muscle), it can be tricky for trainees to register when it has fully recovered in order to correctly and specifically train it. Since the phosphagen system is required for “emergency” energy production, snapping into action immediately upon the initiation of any activity, it can take several minutes to truly allow it to recover back to its resting state. The pool of ATP and creatine phosphate molecules must be resynthesized in order to be prepared to take on a similar max effort. This can take several minutes to accomplish depending on the degree of depletion by the end of the first bout of exercise. A rule of thumb is to allow anywhere from 2-5 minutes of rest to get as close to a full recovery as possible.
Resistance training the phosphagen typically produces the highest degree of strength, explosivity, and has a synergistic effect on muscle building. That said, the phosphagen system is acting in continuous synergy with the other energy systems. It bridges the gap in start-up time required for the slower but more sustainable energy systems to begin dominating energy production. It can also contribute to short bursts of heightened intensity in the middle of slower paced events (example: the sprint at the end of a distance race).
Depending on exercise intensity and duration, along with the glycolytic and aerobic systems, the phosphagen system is in a constant state of activity, recovery, and exhaustion. All three systems exist on a continuum of energy production. To explore this concept, we’ll discuss the glycolytic system next.
Best,
Eric