There are three major sources of high energy phosphate (ATP) that take part in the conservation,
capture, and expenditure of free energy.
These three major chemical pathways, with their common names, are:
- The phosphagen, anaerobic, anaerobic alactic, or ATP-CP system
- Glycolysis, anaerobic lactate, or embden-meyerhof-parnas pathway. This can be
broken down into two sub-categories:
A. Anaerobic glycolysis, fast glycolysis, lactic acid, or anaerobic lactate pathway
Aerobic glycolysis, or slow glycolysis pathway - The oxidative, aerobic, or aerobic respiration system.
The phosphagen system is an anaerobic process, in which no oxygen is present.
Glycolysis is the sequence of reactions that converts one molecule of glucose into pyruvate, with
the concomitant production of a relatively small amount of ATP. The oxidative system, which takes
place in the cell mitochondria, is the most productive source of ATP, but only functions when the
body is abundant in oxygen.
As these three major pathways are explored, it should be noted that these systems all
co-exist, and are active in overlapping energy expenditures. But the quality and quantity of their
usage primarily depends on the intensity and duration of the demand put on the individual’s
musculoskeletal system. The energy systems help to replenish the depleted ATP as muscular
demands develop during exercise. There is a direct relationship between the exercise intensity and
duration, and the energy system that the body uses to supply energy. The following is a detailed
description of each of the energy systems.
The Phosphagen System
The Phosphagen System is active from rest to the beginning of all exercise, and is an
instant source of ATP. This system provides energy at a very high rate, but only for a minimal
duration of time. The main regulatory chemical reactions of the phosphagen system involve
ATP and CP. Even though this system is very efficient when working; its duration limits its
potential. There are very low amounts of ATP and CP stored within muscle tissues and cells. So
continuous, long-duration activities are not sustainable before these stores are depleted, and
in order to provide for the energy demands the phosphagen system needs to be supplemented
by glycolysis or the oxidative systems2. It has been estimated that approximately 5 millimoles
(mmoles) of ATP and 16 mmols of CP are stored in each kilogram of muscle3. When training
the phosphagen system, one should understand that type II (fast twitch) muscle fibers contain
greater concentrations of phosphagens than type I (slow twitch) fibers4. This fact would lead us
to understand that, for certain exercises or sports, we should be specifically training this system.
For example, if we are training a power lifter who has major demands on type II muscle fibers, and
needs the explosive power and strength for a short duration of time, the phosphagen system is a
major contributor to this athlete’s performance.
The steps of the phosphagen system begin at the start of exercise when ATP is hydrolyzed
by the enzyme myosin ATPase to ADP, organic phosphate and energy. This immediate energy is
released for muscular contraction, although an increased ADP concentration activates creatine
kinase, catalyzing the formation of ATP from the breakdown of CP. As exercise continues at high