Eric Roberts explains that muscle grows in any rep range if sets approach failure, but the 6-12 rep zone is optimal because it balances load and volume without joint stress or metabolic burnout. High-rep work causes cardio fatigue and insufficient load, while low-rep work stresses joints and requires too many sets.
Should you be doing light weight for high reps, or should you be doing heavy weight for low reps if your goal is to maximize strength and muscle building? It used to be thought that there were 3 rep ranges you could fall into: 1 to 5 reps, 6 to 12 reps, and 12 to 20 reps. 1 to 5 reps would fall into the strength rep range. 12 to 20 reps would fall into the muscle endurance rep range, and that 6 to 12 reps would be the holy grail of the hypertrophy or muscle building rep range. And this is what we as personal trainers thought for a long time until new research came out. And what this new research showed was it's less important the amount of reps that you're doing. You could train anywhere from 5 to 30 reps. And so as long as you are training close to failure, meaning that those last couple of reps of your sets are really hard, challenging reps, then really you'll be able to build muscle with any rep range. So wait a minute, does that mean the reps that you do really don't matter at all? Nope, I wouldn't go that far. And here's why. Although science tells us you can technically build muscle in any rep range, when you practically apply it to your workouts, there does tend to be an optimal rep range for building muscle. And let's talk about which one. Doing sets in the 15, 20, 30 rep range can have a few drawbacks for building muscle. The first being because you're doing so many reps, you start to get fatigued and go to failure from a cardio or an endurance perspective simply because you get tired doing the movement. You don't end up going close to failure from a strength or muscle perspective. Second, only doing sets with high reps can be very metabolically fatiguing, which would lead to a high rate of you burning out and feeling exhausted, Leading to less performance in your workouts. And number 3, the weight you would have to lift would end up being so light that it again takes you farther away from that close to failure point. And then if you look at that 1 to 5 rep range, while you definitely would be lifting heavy enough to go close to failure, you would also put a lot of stress on your tendons, joints, ligaments, leading to a higher risk of injury as well as because you're doing so few reps, You would have to do a lot of sets to get the volume necessary to build muscle, which would again put you in that state of burnout and fatigue, making it harder for you to recover and see progress in your workouts. Thus leading us right back to that 6 to 12 rep range. With this rep range, you're able to lift heavy enough weight to stimulate your muscles and strength without overly stressing your joints. And without doing so many reps that you end up turning it into more of a cardio-based workout. So while this proves that the 6 to 12 rep range is actually the best range for building muscle, does that mean this is the only rep range you should be doing? No, it doesn't. And here's why. While I believe most of your sets should come in that 6 to 12 rep range, I would also encourage you to include sets in that 3 to 6 rep range. So that you can get stronger from those sets to be able to lift heavier weight in your 6 to 12 rep range, which will allow you to build more muscle. And then doing some sets in the 12 or 15 or 20 rep range will allow you to have better endurance in your sets so that you can push through fatigue, be able to maintain proper form, and go even closer to failure. Preferred way of setting this up in your workouts is exactly what I do inside of my clubhouse, where your first bigger compound movement of the day— squat, bench, deadlift, shoulder press— is going to be in that lower rep range with heavier weight. And then the following 3 to 4 exercises are going to fall in that 6 to 12 rep range, with maybe your last 1 to 2 isolation exercises falling in that 12, 15, or 20 rep range. This way you can get the benefits of all of the rep ranges leading to the best muscle growth possible for you.
