With tons of research being done in this field, it is a well-established fact that there is no one answer, when it comes to determining the best rep range for bodybuilding. Researches have proven that the best strategy to get the optimal muscle growth is by incorporating a wide variety of rep ranges in your workouts. The main intention behind this is to shock the muscle and force it to grow.
We are aware that human body is highly adaptable. If you train your muscle in a certain rep range, after few weeks the body gets used to it and will stop growing. So it is important to train in a variety of rep ranges and techniques for optimal muscle growth.
Another thing worth mentioning is that the fibers of human muscle tissue is primarily of two types – Fast twitch muscle fiber and slow twitch muscle fiber. In order to break the fast twitch muscle fibers, you need to train them with heavy weights and in low rep ranges. While the slow twitch muscle takes more time to get exhausted and thereby it best to train them with lighter weights and higher rep ranges. This will help develop both the muscle fibers and thereby get the optimal muscle growth.
Ideally speaking 1–5 for strength, 8–12 for mass, and 15+ for muscular endurance are the widely used rep ranges. So you may choose your rep ranges as per your goals.
However, if your goal is to see the best results when muscle growth is in question, you need to optimize all three of these advanced methods and keep shocking your muscles by training them in a variety of rep ranges. The sky is the limit!