How and when are the different sources of muscle metabolism that you already know about...

Once the ATP is used up by the muscles, muscle use up a high-energy phosphate compound called creatine phosphate. The phosphate group is removed from creatine phosphate by an enzyme called creatine kinase, and is transferred to ADP to form ATP. The cell turns ATP into ADP, and the phosphagen rapidly turns the ADP back into ATP. As the muscle continues to work, the creatine phosphate levels begin to decrease. Together, the ATP levels and creatine phosphate levels are called the phosphagen system. The phosphagen system can supply the energy needs of working muscle at a high rate, but only for 8 to 10 seconds.

Anaerobic glycolysis exclusively uses glucose converted primarily from glycogen as a fuel in the absence of oxygen or more specifically, when ATP is needed at rates that exceed those provided by aerobic metabolism; the consequence of rapid glucose breakdown is the formation of lactic acid (more appropriately, lactate at biological pH levels). Physical activities that last up to about thirty seconds rely primarily creatine system. Beyond this time both aerobic and anaerobic glycolytic metabolic systems begin to predominate.

Finally, during aerobic exercise, glycogen is broken down to produce glucose, which then reacts with oxygen (Krebs cycle) to produce carbon dioxide and water and releasing energy. In the absence of these carbohydrates, fat metabolism is initiated instead. The latter is a slow process, and is accompanied by a decline in performance level.

Show the relationship between heat production and muscle use.

The more your muscles are used, the more heat is produced. The muscle converts the free energy of ATP into work and heat. According to the 2nd Law of Thermodynamics, energy conversion always generates "useless" energy; entropy increases. If you're breaking down ATP into ADP, you release energy.