A little info on energy pathways
In the human body energy production is centered around ATP. Our muscles can generate ATP by the use of three metabolic pathways. These pathways are the ATP/CP pathway, Glycolytic pathway and Oxidative pathway. Muscle cells can use one or a combination of the three pathways to generate energy. Different forms and durations of exercise cause different demands on the body leading to different ways the body has to generate ATP.
The ATP/CP pathway is anaerobic meaning it does not require oxygen to produce the energy. This pathway is used in exercise that requires quick explosive movements that are high intensity but short in duration. Examples include throwing, jumping, and weightlifting. Since a limited amount of ATP is stored in muscle cells the body must replenish ATP through the ATP/CP pathway. All forms of exercise use this pathway first regardless of the intensity or duration but it only takes under 2 seconds for ATP stores to become depleted and less than 60 seconds for the CP stores to become completely depleted.
The Glycolytic pathway is the second pathway that comes into play. Similarly to the ATP/CP pathway the Glycolytic pathway is also anaerobic. This pathway works by breaking down stored carbohydrates in the muscle cells (glycogen) or available glucose in the blood stream to convert ADP to ATP. The limiting factor becomes the byproduct of the ADP-ATP conversion which is lactic acid. This pathway is the main form of energy production between the 60 and 80 second mark. The Glycolytic pathway is used mainly during weight lifting repetitions, repeated jumps or throws lasting under 80 seconds in duration.
Finally the Oxidative pathway, the only pathway that is aerobic meaning it requires oxygen to produce ATP. This process produces the most ATP however it also takes the longest. Endurance training uses this form of energy. Long distance running, biking or rowing will cause this energy pathway to come into use. This pathway will continue for the duration of the exercise breaking down carbohydrates and fat until they are no longer available and then it will start breaking down muscle (amino acids) for energy.