Energy for Exercise: Adenosine Triphosphate (ATP) and Energy Transfer

Adenosine Triphosphate (ATP)

ATP is the primary source of energy for all cellular processes including muscular contraction during exercise.
It consists of an adenosine molecule and three phosphate groups, which store high amounts of energy.
The breakdown of ATP into Adenosine Diphosphate (ADP) and a separate phosphate molecule releases the energy stored within these bonds.
This provides the energy for muscle contraction, allowing movement and exercise.
However, the body only stores enough ATP for a few seconds of intense exercise, so it needs to be constantly resupplied.

ATP can be resynthesised from ADP and Phosphate through three metabolic pathways: the ATP-PC system, the Glycolytic system, and the Oxidative system.
The ATP-PC system, also known as the phosphagen system, is the most immediate and fastest way to resynthesize ATP. This anaerobic process primarily fuels short, high-intensity activities such as sprinting or powerlifting.
The Glycolytic system, or anaerobic glycolysis, breaks down stored carbohydrates (glycogen) or blood glucose into pyruvate to produce ATP. This also occurs without the need for oxygen and predominantly fuels moderate to high-intensity exercise lasting up to a couple of minutes.
The Oxidative system, or aerobic metabolism, utilises either carbohydrates (in the form of glucose) or fat to produce ATP with the aid of oxygen. This is the primary system used in low-intensity, prolonged activities such as distance running or cycling.

The type of exercise performed will dictate which metabolic pathway is predominantly used to transfer energy through ATP resynthesis.
Short, explosive exercises will utilise the ATP-PC system due to the immediate need for energy.
Activities of moderate to high intensity and short duration (up to a few minutes) will predominantly use the glycolytic system.
Longer duration, lower-intensity exercises will primarily utilise the oxidative system, making use of the body’s larger fat stores and oxygen availability.
Individuals training to optimise performance in specific activities need to understand which energy systems are most heavily relied upon in those activities and target their training accordingly.