The easiest way to understand this is to ask it from the opposite perspective — what would you need to do if (heaven forbid) you actually wanted to look like Helga the Hulk? The answer would be that you should aim to lift heavy weights.
How to tone the muscle
If you want to avoid transforming yourself into a lumberjack, do the opposite — lower weights with more repetitions. This shifts the physiological response away from bulking up, and towards toning the muscle.