An energy-carrying molecule known as adenosine triphosphate (ATP) fuels every living thing — you, me, plants, animals, all of it — and, when you get right down to it, it's what fuels your second wind.
Adenosine nucleotides are part of the energy production systems of your body, specifically the energy metabolism of your cells. ATP is created from the process of metabolizing the carbohydrates, fats and proteins you consume. It's formed by a high-energy bond between lower-energy phosphates, adenosine diphosphate (ADP) and inactive phosphate (Pi).
The body makes an ongoing supply of ATP, and it starts with the breakdown of sugars from food. First, a reactive process called glycolysis traps and converts glucose, a monosaccharide, and converts it into fructose 1,6-bisphosphate. Next, that fructose 1,6-bisphosphate is split into two molecules of three-carbon pyruvic acid (CH3COCOOH); that's important, because ATP is produced when those three-carbon molecules are oxidized into pyruvate, the final product of the glycolysis energy-conversion process. In short, your body is constantly breaking down the food you eat and converting it to stored energy, which can fuel that second wind.
Because ATP is critical and stored only in limited amounts, the process of hydrolysis and resynthesis is circular and ongoing. ADP and Pi combine to synthesize and replenish the body's ATP, and through hydrolysis, ATP is broken down into ADP and Pi as needed for energy. That equation that looks like this: ATP + H2O → ADP + Pi + energy [source: Encyclopedia Britannica].