Most people are somewhat familiar with the association between exercise reps ranges and their targeted effect on the body during resistance training. The heaviest load one can lift at a given weight correlates with maximal strength, while anything one can do above 20 times or more clearly signifies muscular endurance.
Somewhere between these two ends of the spectrum, however, lies muscular hypertrophy. Some coaches and trainers contend that ten reps are the magic number, while others believe a range of 8-12 is more accurate. So, what is it? Will I grow huge biceps if I do 4 sets of 8 or 3 sets of 12?
Quite honestly, it doesn’t matter, there is no magic window, and the answer is more complicated than one may think.
How Does One Gain Muscle?
While you might already be scratching your head wondering why rep ranges aren’t as big of a deal for gaining muscle as you’d previously thought, it’s important to understand how muscular hypertrophy occurs in the first place.
There are three main ways that one can enhance muscle protein synthesis via the mTOR pathway resulting in an increased muscle cross-sectional area.1
The first way is through increased muscular tension, which occurs through using a heavy load while performing an exercise through a full range of motion. As a muscle spends more time under a given weight, and then the load increases, this increases the time under tension (TUT).2 Through the use of slower tempos, pauses, and increased weight, one can dramatically increase their TUT in a given exercise. The second method to increasing muscular hypertrophy is through muscular damage, most often associated with severe soreness or the delayed onset muscle soreness (DOMS) one feels multiple days after a hard training session.2
This soreness occurs because of small micro-tears within the muscle fibers themselves, especially during eccentric and concentric muscle contractions. When given adequate time to recover and proper nutrition, the muscle fibers repair themselves and allow one to handle a slightly more significant stimulus the next time around. The third method with which muscular hypertrophy occurs is through metabolic stress. This stress often occurs through the use of lighter weights at a higher given rep range and is associated with the burning sensation one feels while lifting.2
As the muscles continuously contract and relax, blood pools and muscle cell swelling occurs.1 This metabolic stress restricts blood flow and ultimately induces muscle hypoxia, which in turn, allows for the metabolites, such as lactate and hydrogen ions, to build. These metabolites induce an anabolic effect, which leads to molecular cell signaling for increased hormonal responses on the body.
Each of these three methods plays off of one another and should be used in a complementary fashion to yield the best training results possible.
Understanding what drives muscular hypertrophy from a physiological standpoint easily explains why subscribing to an arbitrary rep range is sub-optimal for training.
Through the manipulation of the three previously mentioned variables, one can control the volume load they are training with, which is perhaps one of the most important considerations of all when seeking muscular hypertrophy.
Volume load is a simple formula that you can calculate as:
Sets x Reps x Load = Volume Load
Increasing volume load through a properly periodized program will ensure that more significant stimulus is being placed on the body and ultimately driving adaption.
Take, for example, the previously mentioned reps/sets count of 4 x 8 or 3 x 12. If I lifted 4 sets x 8 reps x 100 lbs, that would be 3,200 lbs versus 3 sets x 12 reps x 100 lbs, which would be 3,600 lbs.
My 3 x 12 would likely yield more significant results with all things being equal, such as tempo and TUT, because it’s a larger stimulus.
Now imagine that I did 4 sets x 8 reps x 150 lbs = 4,800 lbs, versus 3 sets x 12 reps x 120 lbs = 4,320 lbs. Theoretically, my 4 x 8 would be better for muscular hypertrophy.
You can see that the rep range is only one factor in the equation, meaning that increased volume load can be achieved in a variety of ways with no magic rep range genuinely existing.
What is interesting, however, is that somewhere in the 8-12 rep range still appears optimal for inducing muscular hypertrophy because it strikes a balance between moderate weight at a reasonably high rep range.3
Attempting to do 50 reps with 10 lbs will only result in a 500 lbs volume load, whereas 5 reps at 100 lbs could achieve the same result in less time.
Conversely, it would take 10 sets of 1 repetition at 300 lbs to reach 3,000 lbs.
In contrast, 3 sets of 10 repetitions at 100 lbs would equal the same volume load despite it requiring a much more extended rest period between sets for the 300 lbs single repetition sets.
Remember, however, that this relates to muscular hypertrophy. Volume load, while necessary for muscular strength, does not play nearly the same role as it does for gaining muscle.
Additionally, one can only handle so much volume before one will inadequately recover. That is another article for another day.
All in all, I hope that you have a greater understanding of how muscular hypertrophy occurs and how you can manipulate your training. You mustn’t get stuck in a dogmatic routine following an arbitrary rep count simply because that’s what you’ve always thought was best.
Doing a little research and digging for more in-depth answers is vital if you truly want to get a grasp on how training works. Thank you for reading, as always.
1. J Jones E, Bishop P, K Woods A, and Green J. “Cross-sectional area and muscular strength: a brief review.” Sports Medicine (Auckland, NZ) 38: 987-994, 2008.
2. Hornsby WG, Gentles JA, Haff GG, Stone MH, Buckner SL, Dankel SJ, Bell ZW, Abe T, and Loenneke JP. “What is the impact of muscle hypertrophy on strength and sport performance?” Strength & Conditioning Journal40: 99-111, 2018.
3. P. Loenneke J, Dankel S, Bell Z, Buckner S, Mattocks K, Jessee M, and Abe T. “Is muscle growth a mechanism for increasing strength?” Medical Hypotheses 125, 2019.