Energy, How Does My Body Get It and How Does It Use It?

Many times people will ask an energetic person they know, where do you get all that energy from?? We just assume they simply have an overactive and limitless supply of energy which we are just not capable of having ourselves. We may ask ourselves, why is it that when I exercise I seem to run out of gas and get tired after thirty minutes but that guy over there seems to be able to keep at it for well over an hour without tiring out? Is he just a more energetic person than me? Why can