The phrase "balls to the wall," meaning an all-out effort, sounds as if it is a reference to a part of the male anatomy, giving rise to some confusion as to what it originally meant. However, the original usage has nothing to do with anatomy, coming rather from the world of aviation.

On an airplane, the handles controlling the throttle and the fuel mixture are often topped with ball-shaped grips, referred to by pilots as (what else?) "balls." Pushing the balls forward, close to the front wall of the cockpit results in the most and richest mixture of fuel going to the engines and the highest possible speed.

The phrase dates to the early 1950s.