I'd like to know the meaning of "leverage" in this extract from the first chapter of The Great Gatsby:
Not even the effeminate swank of his riding clothes could hide the enormous power of that body—he seemed to fill those glistening boots until he strained the top lacing and you could see a great pack of muscle shifting when his shoulder moved under his thin coat. It was a body capable of enormous leverage—a cruel body.
Leverage means having the mechanical advantage of a lever. In other words, if I am trying to move an object, I want to position myself at an angle in which I can act as a lever; this might require me to crouch down or angle myself in order to get a more balanced stance. When Nick describes Tom's body as "capable of enormous leverage," he means that Tom has an athletic body type, built so as to give him an advantage over someone that is small and frail or someone too tall and lanky. Tom had been a very good football player, so he had already proven that he could use his body in powerful ways. Since Nick notes that Tom's body was a "cruel body," the reader gets a possible glimpse of Nick's assessment of Tom's personality in addition to his powerful body.
In the line previous to this quote, Nick adds:
Two shining arrogant eyes had established dominance over his face and gave him the appearance of always leaning aggressively forward.
So, Tom has the physique that would give him more leverage (more mechanical/physical advantage over others) but Nick's descriptions also indicate that this potential for Tom to have physical leverage says something about his personality: that Tom might be prone to violence and aggression. (We see later that this is true when he breaks Myrtle's nose.) In the previous quote, Tom appears to Nick to always be leaning forward; again, this shows Tom's personality as being aggressive, establishing his advantage as the aggressor and in this sense, having physical leverage as well as trying to establish psychological leverage over others.