Where does energy come from?
The energy currency that is in our body is called ATP (Adenosine triphosphate). It is a compound made up of 1 adenosine molecule bound with 3 phosphate molecules with high energy bonds between them. ATP is what every cell in our body needs to survive. Our macronutrients such as carbohydrates, protein and fat play an important role in production of ATP. Therefore, it is essential to eat a balanced amount of macros to nourish our bodies enabling us to have sufficient energy.
The ATP and ADP cycle
When we start to exercise, ATP get rids of 1 phosphate molecule. This phosphate molecule goes to create a muscle contraction. What remains once the phosphate molecule has left is ADP (Adenosine diphosphate), which consists of 1 adenosine and 2 phosphate molecules. When you rest during your workout, ADP gets converted back to ATP via adding 1 phosphate molecule and your energy is replenished.
Concise explanation:
When you begin to exercise: ATP - P = ADP
During rest period, ATP is replenished: ADP + P = ATP
This is a never ending ongoing cycle.