In the past, it sometimes led to discussions in the locker room: which rep range is best for muscle growth? By now, we know better: you can achieve maximum muscle growth over a very wide range. New research confirms this.
THE RESEARCH
The study was conducted among twenty healthy young male participants who performed strength training three times a week for ten weeks. In each participant, the arms and legs were trained using bicep curls and leg tensions, respectively. This was performed unilaterally: one side with a heavy weight (8 to 12 repetitions), the other side with a light weight (20 to 25 repetitions), always with three sets to muscle failure. Afterwards, ultrasound measurements of muscle growth and measurements of protein synthesis determined that light and heavy training weights achieved the same muscle growth.
The research confirms what we have known for a long time: for muscle growth, you can use any training weight between roughly 4 and 30 repetitions, as long as you train close to muscle failure and as long as that training weight is your starting point for making progress.
HOWEVER, WE HAVE A PREFERENCE
In principle, any rep range is suitable for muscle growth, but very low ranges (< repetitions per set) or very high ranges (> 20 repetitions per set) have their specific disadvantages and may therefore not be optimal.
If you want to lift very heavy most of the time (< 5 repetitions per set), you may need to do more sets to get the sufficient volume required to cause muscle growth.
If you want to lift lighter weights most of the time (15-20+ repetitions per set), you must accept experiencing more pain and discomfort than with a medium-rep range, for example, 8 to 12 repetitions. As a result, cardiovascular fatigue will be significantly higher. One study reported that the sensation of discomfort was considerably higher at approximately 20 repetitions per set compared to 10 repetitions per set. Another study shows that training at a lower intensity leads to more neuromuscular fatigue, loss of strength, and recovery time than training at a high intensity, assuming that training is performed near muscle failure in both cases. Incidentally, for optimal muscle growth, the weight must be greater than 30% of your 1-rep max (1RM).
Our preference is therefore for the middle ground: 6 to 15 repetitions, of which 6-10 for compound exercises and 10-15 for isolation exercises. The latter is to avoid overloading muscles when they are working alone.
Does that mean high-rep work is written off for muscle growth? Not entirely. The major advantage of training with light weights is that they are gentle on your joints and other connective tissue. This is useful if you have (had) an injury. Additionally, training with many repetitions creates metabolic stress, which in itself could be a path to muscle growth. Finally, you burn more calories with long sets, which can be useful in an all-in-one program for both muscle growth and fat loss.
There are arguments why, as an advanced strength athlete, you could also do some sets in the ranges of 3-6 and 15-30 repetitions.
CONCLUSION
You can achieve optimal muscle growth with a very wide range of rep ranges. For practical reasons, it is best to train primarily in the range of 6 to 15 repetitions, keeping an average of 1-3 repetitions ‘in the tank’ (1-3 RIR).
As an advanced trainee, you can also introduce some variation in the rep ranges used. Incorporate different rep ranges into a single training program (meaning no block periodization). Keep 60-70% of that program within the traditional range of 6 to 15 repetitions.