Creatine is one of the most talked-about ergogenic aids around. A number of supplement companies offer creatine monohydrate (CrH2O) as a new tool for increasing strength and muscle mass.
The Role of ATP
All of the energy produced by the body is generated through a series of chemical reactions within the body's tissues. The raw materials for these reactions are the foods we eat: the carbohydrates, fats and proteins. These foods are by and large digested in the stomach and assimilated in the intestines. Many go through additional chemical changes in the liver. These components are then converted by a series of reactions into a chemical called adenosine triphosphate, or ATP
ATP is known as the body's "energy currency" It's used for building new tissue, nerve transmission, digestion, gland secretions and, of course, for muscle contraction. As its name implies, ATP has three phosphate molecules bonded to an adenosine molecule. When one of the bonds connecting these phosphate molecules is broken through a process known as hydrolysis, a great deal of energy is created. It is this breaking of bonds between molecules that produces all of the energy utilized by the body. In muscle the energy activates specific sites on the contractile elements of the muscle fiber, causing them to shorten.
There are three main pathways for the energy production the body needs to live and grow. This energy is produced by complex reactions that occur within the cell, and all involve the use of ATP in differing ways. Two of these three pathways are called anaerobic, which means that the chemical processes producing the energy do not utilize oxygen. The anaerobic pathways include the ATP-CP system and glycolysis. The third pathway utilizes oxygen in its chemical reactions and is referred to as the aerobic system. Only the ATP-CP system uses creatine to create energy.
The ATP-CP Energy Pathway
The ATP-CP pathway is the body's only immediate source of energy. Activities such as weightlifting and the 100-yard dash, which require rapid and immediate energy, are heavily dependent on this pathway. The ATP-CP system involves an interaction between two molecules, ATP and creatine phosphate, or CP, within the cell. When ATP's outermost phosphate bond is broken off, adenosine diphosphate, or ADP, is formed, along with a great deal of energy. Since the body has only about three ounces of ATP at any one time, however, it runs out of its supply rapidly. Creatine phosphate comes to the rescue. The CP molecule also releases a large amount of energy when the bond between its creatine and phosphate molecules is split. As a result, its phosphate is donated directly to ADP to re-form ATP in the presence of the catalytic enzyme creatine kinase. This process is known as rephosphorylation. ATP is now available to begin the energy cycle again. Since the cell's concentration of CP is three to five times higher than that of ATP, creatine phosphate functions as the cell's energy reservoir.
The ATP-CP pathway provides enough energy for a one-minute walk or six seconds of sprinting, after which the other pathways take over. The main advantage of this energy system is that it can go to work immediately, something the others can't do. If it weren't for the ATP-CP system, we wouldn't be able to lift heavy weights or do any other work that requires immediate full effort. We'd have to start lifting in slow motion.
The Other Energy Pathways
The second anaerobic system is glycolysis. This system provides most of the energy for medium-duration activities like bodybuilding, wrestling and sprint swimming. During glycolysis a glucose molecule enters the cell from the blood and is transformed into a product called pyruvic acid through a series of complex reactions. These reactions allow a significant amount of energy to be produced quickly for muscular contraction just as the ATP-CP system begins to phase out. Glycolysis can also use muscle glycogen (the stored form of glucose) and the glycerol formed when a fat molecule is broken down as raw material for energy production.
In the absence of adequate oxygen the pyruvic acid is converted into lactic acid and alanine, which actually helps keep glycolysis going by removing excess hydrogen ions that would normally bring it to a halt. The lactic acid escapes into the bloodstream and away from the muscle. This escape mechanism is only temporary, however, because the level of lactic acid in the blood and muscle eventually increases. This increased acidity inactivates some of the enzymes used in glycolysis, which reduces the ability of the muscles to contract. Fatigue sets in and exercise must stop.
The third type of energy production is the aerobic system, which is used for vigorous exercise beyond two to three minutes. This system releases 95 percent of the potential energy in each glucose and fat molecule through a complex set of processes called the Krebs cycle, which can only function in the presence of oxygen. This aerobic system makes use of the mitochondria in the cells, which are also known as the cells' energy factories
All three energy systems are interrelated. Rather than switching on and off like the lights of a traffic signal, they overlap to provide a smooth transition from one means of energy production to another. This allows the body to perform at its best through all levels of exercise intensity. Creatine compounds play an important role in the process by providing large amounts of energy for immediate use.