Sure, lots of guys at your local gym want to get as unbelievably jacked as possible. But believe it or not, not every athlete wants to build massive muscles.
Consider gymnasts, who use their own body weight as their primary resistance. They need strength, but additional bulk can be more of a hindrance than a help. Likewise, athletes who compete in weight classes—like wrestlers, MMA fighters, boxers, and competitive weightlifters—want to be as strong as possible while trimming away any unnecessary weight.
So how to gain strength without the size?
First, remember that strength isn't solely a property of muscle, but rather a property of the neuromuscular system. So going for the "pump"—total muscle exhaustion and complete muscle annihilation—is not the name of the game here. Your body increases its strength by a) recruiting more muscle fibers in a particular muscle group and b) increasing the firing frequency of your motor neurons (neurons and muscle fibers). Apply these methods below to increase your strength without inflating yourself.