How Many Reps to Build Muscle vs. Strength?

How many reps should you do to build muscle vs. strength?

The number of reps you do greatly influences your training results in terms of hypertrophy or strength gains.

Here’s a summary of our recommendations:

Number of Reps to Build Muscle:

Anything between about 5–40 reps per set (between about 40–85% of 1RM) has been shown to be effective in building muscle. More or fewer reps than that and the muscle-building effect per set decreases somewhat.
For practical reasons, it is a good rule of thumb to aim for about 8–15 reps per set for muscle growth. Here, the muscle-building effect is large, and it is quite easy to tire out your muscles.

Number of Reps for Strength:

About 1–5 reps per set (>85% of 1RM) is probably most effective for strength.
Up to about 10–20 reps per set (~60% of 1RM) is moderately effective for strength, but any lighter than that and the strength gain is small.

Note that these numbers apply to sets taken to, or close to, failure. That is, the point where you no longer can do another rep.

That’s the short version of this article. For the longer version, keep reading!

How Many Reps Should You Do?

How much weight you lift when you train and how many repetitions you do, is one of the most important factors for what results you will get from your training.

A high number of repetitions with light weight give you different results than if you do few repetitions with a heavy weight.

The heaviest weight you can lift in one repetition is called your 1RM – 1 repetition maximum. The lighter the weight in relation to your 1RM, the more repetitions, or reps, you will be able to do in one set.

Exactly how many reps you can do on a given percentage of your 1RM depends on many variables, such as:

The exercise. Can you rest at the top or bottom of the exercise (as in deadlifts)? What does the movement path and the force curve look like?
Muscles. Is the exercise performed by muscles that are primarily fatigue resistant or explosive?
Genetics. What does your individual muscle fiber type distribution look like?
Training. What have you practiced the most? Have you trained with mostly a high or low number of repetitions?

The table below shows some averages for the number of reps most people can do on a given percentage of their 1RM.

How many reps at different percentage of 1RM — Typical values of how many repetitions you can do at different % of 1RM. Note that the variation is large depending on exercise, the individual and training background.

You can use our 1RM calculator to calculate an estimate of your one-rep max.

Now – depending on how heavy you lift and how many reps you do, your muscles will be activated differently.

You Must Do Enough Reps to Stimulate All Muscle Fibers

There are thousands of small muscle fibers in your muscles. These are recruited as needed and in increasing size: the small ones are activated first when the need for muscle power is small. But as you lift heavier loads, more and larger muscle fibers are activated. When you lift the maximum of what you’re capable of in a single lift, virtually all muscle fibers are activated simultaneously.

In addition, your muscle fibers cooperate, relieving each other of work as they get tired.

Let’s say you do a set at 60% of 1RM, where you normally manage about 20 repetitions.

At the beginning of the set, only some of your muscle fibers need to contract to lift the weight.
After a few reps, the first muscle fibers begin to tire and lose strength, and other, larger and stronger muscle fibers join in to help to generate force.
As the set goes on, more and more muscle fibers are exhausted, and more are recruited to join in. And after a while, there are not enough rested and strong muscle fibers available to generate force enough to lift the weight, and the set is over. You have reached failure, the point where you can’t lift the weight for another rep.

Only the muscle fibers that work and generate force will grow. If they contract hard enough for a sufficient number of times, the growth process is started.

How Many Reps to Build Muscle?

To build muscle, you must stimulate muscle growth by loading and/or tiring out your muscle fibers. The more muscle fibers you stimulate, the more that muscle will grow.

Two common pitfalls can inhibit muscle growth when it comes to the number of reps and choice of weight are:

Doing too few reps with a too light weight. Let’s say you pick a weight that you could do 20 reps with, but you only do five. In that case, only a small number of your muscle fibers would be recruited and used, and they would probably not even be particularly exhausted either. If you would continue the set, you would gradually recruit and exhaust more muscle fibers. If you had done about 17–20 reps, most of your muscle fibers would receive a good training stimulus.
Using too heavy weight. Assume instead that you pick a very heavy weight, which you can only lift for a single repetition. All of your muscle fibers will contract maximally from the start, and when you’re finished with the first repetition, your strongest and most explosive muscle fibers will be exhausted. Your weaker but more fatigue-resistant fibers, on the other hand, are hardly tired at all, but they cannot lift the heavy weight and continue the set on their own. In this case, you have picked a weight where you can no longer continue the set as soon as only your strongest muscle fibers are exhausted.

Effective training for building muscle requires you to use a sufficiently heavy weight, and train sufficiently close to failure with it. You don’t need to go all the way to failure (that could even be detrimental to your growth if done in exaggeration), but you should train within a couple of reps (~1–3) from it.

So, what is a sufficiently heavy weight, then?

As we mentioned in the introduction, and as will be seen from the research we will soon take a closer look at, a weight where you can do about 5–40 reps per set seems appropriate for building muscle.

For practical reasons, about 8–15 reps per set may be better to aim for. It does not require as much energy and pain as a set of 40 reps, and it may be a little easier to tire out your muscles more thoroughly with a slightly lighter weight than one you can only do five reps with.

Bodybuilder training biceps — Bodybuilders typically train with a medium number (about 8–15) of reps per set to build muscle.

How Many Reps for Strength?

When it comes to training for strength, the importance of tiring out every single, little fatigue-resistant muscle fiber decreases.

Instead, the importance of training the biggest and strongest muscle fibers (which may not be so fatigue-resistant) increases. And above all, it becomes important to train your neuromuscular system which ensures that not only all muscle fibers but also all interacting muscles in the exercise are contracted as powerfully and coordinated as possible.

And you seem to train this best by simply practicing lifting heavy.

Training with weights where you can do about 1–5 reps per set (>85% of 1RM) seems to be the most effective for strength, but training with weights up to about 10–20 reps per set (~60% of 1RM) is still moderately effective. Lighter than that, and the strength gains diminish.

Note that this applies per set. Although a single rep at 100% may be the training that per set gives you the best return in the form of strength gains, you might be able to do more sets with slightly lighter weights and more reps. Each individual set might not be as effective, but all sets taken together still gives you a better result than the heavy single.

Powerlifter training for strength — Powerlifters typically train with a low number (about 1–5) of reps per set for strength.

The Best Number of Reps for Strength vs Hypertrophy

Let’s look at the research investigating how different numbers of reps per set affect your strength and muscle hypertrophy.

This will give you a better understanding of how big the difference in results is when training with a low or high number of reps.

Training With 20, 40, 60 or 80% of 1RM

One study had participants train bicep curl and leg press with 20, 40, 60, or 80% of their 1RM for 12 weeks.¹

The three groups training with 40, 60, and 80% of their 1RM (about 8–40 repetitions per set) all gained similar amounts of muscle.
The group training with 20% of 1RM (about 50–85 repetitions per set) only built half as much muscle.

The diagram below shows the muscle growth in the biceps and quadriceps after 12 weeks of training at different reps numbers.

As for the increase in strength, the results were not quite as even:

The two groups training with the lightest weights (20 and 40% of 1RM) saw smaller strength gains than the groups training with heavier weights.
In the bicep curl, the increase in strength was greater the heavier weights the participants trained with, but in the leg press, the increase in strength was slightly greater for those who trained with 60% of 1RM.

Is 3 x 3 or 3 x 10 Reps Better to Build Muscle or Strength?

Another study compared two classic approaches with each other: 19 participants got to train either:

3 sets x 3 reps, or
3 sets x 10 reps

More precisely, they should fall between 2–4 and 8–12 reps in their sets, respectively.²

The participants’ 1RM was tested in the squat and bench press and the muscle thickness in the biceps, triceps, and quadriceps was measured before and after the training, which was carried out for eight weeks.

After eight weeks, both groups had increased their muscle mass and strength. However, the group that did 2–4 reps per set gained slightly more strength, and the group that did 8–12 reps per set gained slightly more muscle mass.

Is 8–12 or 25–35 Reps Per Set Better to Build Muscle and Strength?

In another study, 18 participants got to train three full-body sessions per week for eight weeks, with seven exercises per session and three sets per exercise.³

One group did 8–12 reps per set.
The other group did 25–35 reps per set.

Muscle thickness was measured in the biceps, triceps, and quadriceps, and 1RM was tested in the squat and bench press.

After eight weeks of training, both groups had gained similar amounts of muscle, but the group training with 8–12 reps increased their strength more than those training with 25–35 reps per set.

A Meta-Analysis of 21 Studies on the Best Number of Reps per Set

To get a broader perspective, we can turn to a so-called meta-analysis from 2017.⁴ In this meta-analysis, all training studies with at least two groups of participants who trained with light (<60% of 1RM) or heavy (>60% of 1RM) weights to failure were compiled. 21 training studies were found and included in the analysis.

When the results were compiled, they showed that training with light (<60% of 1RM) and heavy (>60% of 1RM) weights both led to similar muscle growth. However, training with heavier weights (>60% of 1RM) was better for strength than training with less than 60%. The difference wasn’t big, though: the average increase in 1RM among those training with heavy weights was 35.4%, compared with an increase of 28.0% for lighter weights.

Should You Vary Your Rep Range For Hypertrophy?

There is a hypothesis that you can build more muscle by varying the load and number of reps you do, compared to sticking to the same rep range all the time. To my knowledge, this has only been examined in one study.⁵

The study divided 19 trained participants into two groups. Both groups got to train three full-body sessions per week, for an eight-week period.

One group trained with 8–12 reps per set in every workout.
The other group trained with 2–4 reps on workout 1, 8–12 reps on workout 2, and 20–30 reps on workout 3.

After eight weeks, the researchers saw no significant difference in results between the groups: both gained similar amounts of strength and muscle mass.

Personally, I still believe there might be a psychological benefit to varying your rep ranges in this way – at least if you enjoy it. But based on this single, short study, it does not seem to have any earth-shattering effects on your muscle mass compared to just sticking to a medium rep range and trying to lift more weight in time.

Does Light and Heavy Weights Train Different Muscle Fibers?

Could it be that strength training with heavy weights primarily trains type II fibers and light weights train type I fibers and that for maximum muscle growth, you should train in both rep ranges?

There’s a literature review from 2018 that examined exactly this, and in that review, no significant difference was found where heavy or light strength training would make one or the other type of muscle fiber grow more.⁶

For now, it seems that strength training performed with both light and heavy weights leads to the growth of both type I and type II muscle fibers, and somewhat more in the latter. However, the area doesn’t seem to be very well-researched yet, and hopefully, there will be more research on this in the future.

How Many Reps For Strength Endurance?

This article would not be complete without touching on the trait commonly referred to as strength endurance or perhaps muscle endurance. By that, I don’t mean the long-lasting sort of muscle endurance that you train in classic cardio training, but rather your ability to lift light or medium weight for many reps.

This is the type of strength endurance you need when, for example, you are competing in doing a lot of pull-ups, dips, or certain Crossfit events. Not the type of exercise that necessarily is challenging for your lungs and your heart, but the kind that requires that your muscles be able to do many reps, in the order of 20–50 reps approximately.

Just like with any other training, you get better at what you train. This means that if you want to become good at doing many reps of pull-ups, then doing many reps of pull-ups is the training that will give you the highest return, regardless of whether you currently manage 3 or 30 reps.

But what if you currently can do 30 reps, and want to train yourself to be able to do 40?

Then I suggest a two-part approach:

Train specifically for muscle endurance. Train your regular pull-ups with high repetitions. Your muscles will make specific adaptations to that type of work, such as larger glycogen stores, higher capillary density, and other things that provide a better ability to convert energy and to work for a long time. As icing on the cake, you get to train your own pain tolerance and practice the strategy of coping with those kinds of sets. This training will allow you to do more reps on a given percentage of your 1RM.
Train to increase your maximum strength. Train with low reps and heavy weights by adding extra weight to a belt. By increasing your maximum strength, your regular pull-ups will be lighter, relatively, which can lead to you being able to do more reps. This training increases your 1RM so that your regular pull-ups are performed at a lower percentage of 1RM.

If you are going to do many reps at a given weight, it is important to be both strong and fatigue resistant, and with this two-part approach, you train both qualities.

Summary and Practical Application: How Many Reps Should You Do?

In general, the training effects from light and heavy weights (or high and low reps) overlap, with some differences.

You can build muscle with a wide range of repetitions, and it is only if you do very few or very many reps per set that the muscle-building effect decreases.
In the same way, you can get stronger with a wide range of repetitions, but in general, heavy weights with few reps per set give greater strength increases, and with really light weights (many reps per set) the strength increase is small.

We recommend the following number of reps, with the corresponding appropriate load: