Just because they're behind us and we don't see them, doesn't mean that back muscles are not important. Acting like levers and pulleys in the skeleton, back muscles are key to powering the upper and power body through dynamic and static movements. That means that they can often play a key role to increasing power. The Big Back workout works out this very important muscle group so when you feel the need for power your back muscles can back it up.
Extra Credit: Use 16lb+ (8kg+) dumbbells.