rep ranges

[Bio-Active]

Taking the muscle to and past failure is what's important to stimulate growth. Changing your workouts and rep ranges to shock the body every 6-8 weeks is good as well

[Khazima]

Taking the muscle to and past failure is what's important to stimulate growth.

This, strictly for growth what's been shown a lot in the reading I've been doing lately is that the most important thing is to take a muscle near failure for multiple sets per muscle group has shown the best results for muscle growth whether it's 5 reps or 20.

Personally I spend most of my time in the 3-6 range as a powerlifter and the rest of my work anywhere between 8-20 reps depending on the exercise and the goal of the set (heavy/pump/failure/blood flow etc).