The direct object is the concept used to identify the beneficiary part of the verb in the sentence. In other words, the object or noun modified by the action. In our case, the muscles' ability to store energy is one object. Because we are not talking about the muscles. But their ability to store energy. Therefore, the object is a really small one that is expressed with many words.
The Traditional Plot is the structure behind most of the stories and movies you know. It is helpful to know what it is for writing your own stories and identifying every point in a story.
