What is ATP?

I read this today:  "[t]he ability to maintain prolonged exercise is dependent on the ability to match the rate of ATP supply to the rate of ATP utilisation. If this cannot be achieved then the rate of ATP use must fall and power output will decline."

I used to know what ATP was.  Not really.  But, it sounds familiar.  

Apparently, ATP is required for the biochemical reactions involved in any muscle contraction. As the work of the muscle increases, more and more ATP gets consumed and must be replaced in order for the muscle to keep moving. ATP is complex chemical compound that is formed with the energy released from food and is then stored in all cells, particularly muscles. Only from the energy released by the breakdown of this compound can the cells perform work.

Thus, without ATP, the muscles will not work.  There, direct and to the point.  

I then read that "training" increases the "availability of carbohydrate and lipid as substrate to meet cellular needs for ATP resynthesis."  (Why can't these guys speak English?)  I think this means that training leads to physiological adaptations that "make ATP last longer." I put that in quotes because it is my term of of art and should be in quotes.  

But, here is my question:  what adaptations?  What kind of training "makes ATP last longer?"  This time of year, I always ask:  does riding for hours and hours at zone 2 really maximize the type of adaptations that lead to efficient ATP synthesis?