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“How Many Reps for Muscle Size?” A muscle hypertrophy question

When you ask yourself the “how many reps for muscle size” question, do you ultimately see it as an inquisition in how to get from point A to point B? I’m asking this because that is the context in which I see the “how many reps for muscle size” question. In other words, rather than simply thinking that there must be a magic number of repetitions that build muscle size, our ultimate objective is to be capable of moving a heavier amount of weight for a higher number of reps than we can now. Only when we can do that will our muscles get bigger than they are presently.

To most experienced bodybuilders, this is obvious. For some who are new to bodybuilding, it’s something that still needs emphasis. I’ve noticed that inherent within the “how many reps for muscle size” question among some beginners is an assumption that the number of weight lifting repetitions – along with the number of sets performed – will somehow create muscle size while being absent of some other very important factors.

What are those important factors?

What about ‘overload?’ What about progression into higher weights and volumes of weight moved? What about training to just the right amount of intensity without overtraining or under-training? These are all factors of importance that should ultimately determine our overall training strategy for muscle building, along with “how many reps for muscle size.”

“How Many Reps for Muscle Size”: Keep your eyes on the real objective

Surprisingly, even in this age of easily dispensable and acquirable knowledge, there’s much disagreement in the answer to the “how many reps for muscle size” question. You’d think by now we’d have some consensus on the topic based on extensive studies. However, that doesn’t seem to be the case; even the most respected “experts” in the field of bodybuilding seem to have different recommendations.



Adding confusion to this is the fact that some bodybuilding enthusiasts adopt and recommend repetition numbers based purely on associative observation.

What do I mean by that?

I mean that they observe the repetition scheme of an admired top pro bodybuilder and associate that athlete’s extreme muscle mass with the number of repetitions (or other tactics) that he or she claims to be using. While the pro bodybuilder may be currently using 10 or 12 repetitions, this doesn’t necessarily mean that person’s always used that repetition scheme. Nor does it mean that he or she couldn’t arrive at their current point (or beyond) while occasionally using a different reps scheme. It often only reliably means that this is the repetition scheme they claim to be using right now. 

That ties into my previous point. The bottom line for muscle growth is that in order for our muscles to be bigger, we need to be capable of moving heavier weight for a higher number of reps than we’re capable of now. A Mr. Olympia like Ronnie Coleman doesn’t have huge muscles merely because he uses a magic 10 repetitions during his sets; his muscles are huge because he can perform any number of repetitions using weights with which you and I couldn’t count any repetitions. To drive home the point: If Ronnie Coleman can perform five sets of 10 reps of behind-the-neck presses with 225 pounds, it doesn’t matter if in working his way up to that he once did sets of 7-8 reps with 185 pounds. His muscles are huge because of the place he’s arrived with respect to weight/repetitions. But this doesn’t mean the place he’s arrived is clearly indicative of how he got there.

In other words, the “product” we should keep our eyes on is higher volumes with more weight. Any repetition scheme is just a “process” for getting there. And it can be a fluid process that’s open to interchangeability.

“How Many Reps for Muscle Size”: Muscle Fiber Types

In answering the “how many reps for muscle size” question, the topic quickly turns to muscle fiber types. That’s because we have three different types of muscle fibers (or motor units) that are recruited (and thus, stimulated) under different respective repetition schemes:

  • Slow Twitch Fibers: Also referred to as ‘Type l’ fibers or ‘Red Slow-Twitch Fibers.’ They generate energy through aerobic energy transfer and are thus activated during low intensity, long-duration, endurance exercise. Activities such as walking, biking, swimming, and long-distance running will use these fibers and stimulate their primarily mitochondrial and myoglobin makeup.


  • Fast Twitch (Type lla) Fibers: Also referred to as ‘Red Fast-Twitch Fibers.’ The reference to the color ‘red’ in their name comes from the fact that (like slow-twitch fibers) they’re highly oxygenated with numerous capillaries. This is because they are used (and stimulated) by a combination of aerobic energy transfer (to build more ATP) and ‘myofibril contraction.’ These fibers demonstrate a combination of both slow-twitch and fast-twitch fiber traits. 


  • Fast Twitch (Type llb) Fibers: Also referred to as ‘White Fast-Twitch Muscle Fibers.’ The reference to ‘white’ in their name comes from the fact that they’re the least capillary dense of the three. That’s because they derive energy almost entirely from anaerobic metabolism (i.e. energy from the ATP-CP system). These fibers are used when the body is called upon to lift heavy weight for low repetitions. Activities like sprinting, shot-putting, dead-lifting, or bench pressing a heavy weight in which the muscles fatigue at 3-4 reps are all examples of utilization of these fiber types.  


To simplify slightly, a muscle cell can be stimulated to grow in one of two basic different ways:

  1. Myofibril growth: augmentation of the contractile components.
  2. Mitochondrial development: the building of more mitochondria.

The myofibrils are the contractile components of the muscles. They create strength by actually collapsing into each other as they contract. This allows them to shorten and increase in circumference as they are activated. When the myofibrils are called into play with heavy, intense, low repetition sets, the protein filaments (actin and myosin) that comprise them are actually damaged and require protein synthesis for repair.

In contrast, the mitochondria run all along the sides of the myofibrils and are considered the aerobic energy-producing “powerhouses” of the cell. They allow for the muscle cell to produce the aerobic output of daily activity and high repetition contractions through the use of oxygen and ATP (adenosine triphosphate). With intense, high repetition exercise, the cell adapts by building more mitochondria (through protein synthesis) which boosts cellular energy storage and ATP production capacity.


'Muscle Building Repetitions': The number that's optimal is genetically different among bodybuilders and can vary among muscles of an individual's body


Muscles increase in size primarily with myofibril growth. However, some growth can be obtained from mitochondrial development. Furthermore, it’s believed that mitochondrial development helps lay a foundation for myofibril growth over the long term. This, of course, has an influence in answering the “how many reps for muscle size” question.

“How Many Reps for Muscle Size”: Disagreement among the experts

When I became a certified personal trainer through the NFPT, I was surprised by that organization’s textual claims about weight training repetition ranges. In terms of “how many reps for muscle mass”, they basically teach the following:

  • 4-6 reps: Myofibril stimulation by working Type llb/fast-twitch muscle fibers.
  • 12-15 reps: Myofibril and mitochondrial stimulation by working Type lla/fast-twitch muscle fibers.
  • 20-25 reps: Mitochondrial stimulation by working Type l/slow-twitch muscle fibers.

Interestingly, the NFPT recommends that in order to establish a “working training methodology”, we should avoid the repetition ranges of 7-11 and 16-19 respectively.

What’s their reason for this?

They explain that repetitions in the range of 7 to 11 recruit a joint participation of Type llb /fast-twitch fibers and Type lla/fast-twitch fibers and, thus, work neither muscle fiber-type optimally. Similarly, they claim that reps between 16 and 19 will recruit involvement of both Type llb/fast-twitch fibers and Type 1/Slow twitch fibers, working neither type with optimal results.

Whether this very specific recommendation on reps ranges by the NFPT is plausible is open to debate and experimentation. It certainly sits in contrast to the advice of many other experts. Take strength coach Charles Poliquin for example: He advises bodybuilders to use anywhere from 6 to 20 reps depending on variables such as training experience, number of sets, and the particular muscle being worked. Generally speaking, he thinks the lower reps on this scale should be used by experienced bodybuilders and the higher ranges should be used by beginners. He also believes in adding periodization to the strategy of repetition choices. Aside from what he does recommend, he doesn’t designate blocks of reps within these ranges for bodybuilders to avoid, as does the NFPT.

“How Many Reps for Muscle Size”: Is it a genetic thing?

It’s hardly surprising that individual genetic makeup plays a role in the composition and dispersion of muscle fiber type for which each of our muscle groups are comprised. This suggests a compelling role in how many reps for muscle size that each of us might individually chose. You might have predominantly white fast-twitch fibers making up your biceps with a lower number of red fast-twitch or red slow-twitch fibers within that muscle. Similarly, you might have a greater number of red fast-twitch fibers making up your quadriceps muscle than either white fast-twitch fibers or red slow-twitch fibers. Alternatively, you and I could both have an approximate 50 percent mix of two types of fibers throughout most of the muscles of our bodies.

This genetic aspect of muscle fiber type led Arthur Jones to hypothesize that we can apply a simple test for determining how many reps for muscle size. The test consists of finding the one-rep maximum lift of any isolation exercise and determining how many repetitions one can perform with 80% of that weight. As a simple example, if your maximum lift for one repetition on standing barbell curls is 150 pounds, you’d take 80% of that weight and discover how many repetitions you can perform with that weight:

150 lbs. x .08 = 120 lbs.

120 lbs. (max # of repetitions)

If the max number of repetitions you can perform for one set with this submaximal weight is in the range of 4 to 6, then you’ve primarily got white fast-twitch fibers making up your biceps. If the max number of reps come out somewhere in the 8 to 12 range, then you’ve got mostly red fast-twitch fibers within your biceps.

Although this test can be done on any muscle, it’s not without some inherent flaws. The most salient drawback is that even moderately experienced bodybuilder might have already skewed the results with past training. For example, if he or she has had a bias for strength training in the past, the muscles might already have neurological efficiencies built up for this type of training. Conversely, a past bias for higher repetition, aerobic type work will have built up mitochondrial tissue and efficiencies within them. This just means that this test for determining how many reps for muscle is not an exact science, but definitely a tool with which to experiment.

“How Many Reps for Muscle Size”: Concluding with what’s important

When I browse different bodybuilding forums, I can often spot why many people get frustrated with natural bodybuilding. I believe it’s often because they get fixated on elements of subordinate importance. For example, they’ll discuss “how many reps for muscle size” as if there’s a magic number that which, when plugged in, will cause muscle growth in and of itself. They seem to have forgotten (or never realized) that if there’s a weight of an exercise for which they can presently perform 4 sets of 6 strict repetitions, they’ll have bigger muscles when they can take that same weight and perform 4 sets of 10 repetitions. When that successful augmentation occurs, they realize that repetitions are just one component of a bigger puzzle.

It’s putting that puzzle together and getting from point A to point B that my HardBody Success system is all about.



Hi John,

Thank you for stopping by and providing your comments.

Personally, I'd add caveats to both points.

One: Generally speaking, bodybuilding and strength training are two different diciplines. However, we shouldn't ignore that there are cross-relationships between the two and success factors in each respective one can affect the other. For example, muscle hypertrophy definitely requires increases in muscle strength.

Two: Finding "what works for you" is great advice. But I never discount the possibility that whatever's working for me now could be working even better (and more efficiently) with more insightful understanding and better practical execution of that understanding.



At 55 I am having good progress with the amount of weight and size doing sets of 15.

Bodybuilding and strength training are two different diciplines make sure you know the difference.

But more importantly find what works for you, stick to it and disregard the rest.

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