For the first 45 minutes its glycogen, then body fat for the next 45 minutes. If you train for more than 90 minutes you begin to burn muscle and fat.
Carbahydrates
inaerobic
The main store of energy is in the adipose tissue (body fat), with some also being stored in glycogen stores, for bursts of intense exercise.
During intense physical activity, glycogen; which is energy stored in muscle cells, is used during intense muscle contractions.
This type of exercise, during which the body's oxygen need exceeds the lungs' ability to replenish it is called anaerobic exercise -- literally, 'without air.' Exertion of longer duration, during which the body is able to sustain the energy output (and the lungs have the capacity to provide the necessary oxygen for a longer period of time) is known as aerobic exercise.
During intense physical activity, glycogen; which is energy stored in muscle cells, is used during intense muscle contractions.
Energy is the power you have to use during an exercise
mechanical energy
No. You get energy and nutrients by eating food. During exercise the energy is spent
In Anaerobic exercise
as in a surge of energy or power or short bursts of speed or energy.
the amount of energy exercited during an activty or exercise
When you exercise you use your muscles and your muscles contain Glycogen which could be considered your "energy source". during exercise your muscles use glycogen depleting your energy levels making you feel tired.