How Many Reps Should You Do to Build Muscle vs. Strength?

What number of reps is best for building muscle or increasing your strength?

Should you do low reps with heavy weights or high reps with light weights?

In this post we are going to answer those questions, but first, here’s a summary of our recommendations:

Muscle Growth:

  • Anything between about 5–40 reps per set (between about 40–85% of 1RM) has been shown to be effective for muscle growth. 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. Here, the muscle-building effect is large, and it is quite easy to tire out your muscles.

Strength:

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

Note that these numbers apply to sets taken to, or close to (within a few reps of) 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!

Number of Reps and Your 1RM

How much weight you lift when you train, and how many repetitions you do, is one of the most decisive factors for what results you will get from your training. Many repetitions with a light weight give you different results than if you do a 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 repetitions 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?

Even if the variation is large, there are still some averages that can be good to know of. I do not know where the table below comes from, but I think it fits well enough for me to use it as a starting point when I plan training programs and such.

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.

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

Muscle Activation at Different Loads

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 at the same time.

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

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

  1. At the beginning of the set, it’s enough that only some of your muscle fibers contract to lift the weight.
  2. After a few repetitions, however, the first muscle fibers begin to become tired and lose strength, and other, larger and stronger muscle fibers join in to help to create force.
  3. 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 to create 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 create force will grow. If they contract hard enough for a sufficient number of times, the growth process is started.

Muscle Growth Requires Sufficiently Many Reps, at a Sufficiently Heavy Weight

To get good muscle growth, you need to tire out your muscles. The more muscle fibers in the muscle you tire out, the more that muscle will grow.

There are two common pitfalls that can inhibit muscle growth when it comes to number of repetitions and choice of weight:

  1. Too few reps with a too light weight. Let’s say you pick a weight which 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. Would you continue the set, however, then you would gradually recruit and exhaust more and more muscle fibers, and if you would have done about 17–20 reps, then most of your muscle fibers would receive a good training stimulus.
  2. 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 muscle-building training requires you to use a sufficiently heavy weight, and train sufficiently close to failure with it. You do not need to go all the way to failure (that could even be detrimental to your growth if done in exaggeration), but you should train yourself within a couple of reps (~1–3) from it.

Read more: Training to Failure: Implications for Recovery, Strength and Muscle Gains

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 manage about 5–40 repetitions per set seems appropriate. For practical reasons, about 8–15 repetitions may be appropriate 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.

Training for Strength Differs from Training for Muscle Growth

When it comes to training for maximum 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 gains, 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.

What Does the Research Say?

Let’s move on to the research results that form the basis for the previously mentioned recommendations, and some examples of training programs and their results. This will give you a better understanding of how big the difference in results are between low and high rep training.

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

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

It was found that muscle growth was equivalent (and good!) for the three groups that trained with 40, 60 and 80% of their 1RM. In this study, this corresponded to a range of about 8–40 repetitions per set. The group that trained with 20% of 1RM, on the other hand, did about 50-85 repetitions per set, and had clearly poorer muscle growth.

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

Muscle growth from low vs high reps

As for the increase in strength, it was not quite as even. The two groups who trained with the lightest weights (20 and 40% of 1RM) received worse increases than the groups who trained with heavier weights. In bicep curl, the increase in strength was greater the heavier weights the participants trained with, but in leg press the increase in strength was slightly greater for those who trained with 60% of 1RM.

Strength gain from low vs high reps

3×3 vs 3×10?

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 for eight weeks. 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.

During the eight weeks, both groups increased their muscle mass and strength. However, the increase in strength was marginally better in the group that trained 2–4 reps, and the muscle growth was marginally better in the group that trained 8–12 reps.

Muscle growth from 3 vs 10 reps
Strength gain from 3 vs 10 reps

8–12 vs 25–35 reps?

In yet another study, 18 participants got to train three full-body sessions per week for eight weeks, with seven exercises per session and 3 sets per exercise.3 One group did 8–12 reps per set throughout the period, and 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, it was found that both groups had similar muscle growth, but that the group who trained with 8–12 reps had increased their strength slightly more than those who trained with 25–35 reps.

Muscle growth from 10 vs 30 reps
Strength gain from 10 vs 30 reps

A Meta-Analysis of 21 Studies

To get a slightly broader perspective, we can turn to a so-called meta-analysis, ie a kind of article that compiles all studies within an area, 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. By comparison, most people can do about 15–20 reps on 60% of 1RM when they are fresh and rested. 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 gave equal muscle growth. But, training with heavier weights (>60% of 1RM) led to slightly greater strength gains than those who trained with less than 60%. However, the difference was not large: the average increase in 1RM among those who trained with heavy weights was 35.4%, compared with an increase of 28.0% for those who trained with lighter weights.

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 is 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.5

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.

Should You Vary Your Training With Different Rep Ranges?

There is a hypothesis that you can get greater muscle growth by varying the load and repetitions you train with, compared to sticking to the same rep range all the time. To my knowledge, this has only been examined in one study.6

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, however, no significant difference was seen between the groups, but both increased their muscle mass and strength equally.

Personally, I still think there may be a psychological benefit to varying in this way, at least for those who 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 increase the weight you lift.

What About 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 do not mean the long-lasting sort of muscle endurance that you train in classic cardio training, but rather your ability to lift a 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 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:

  1. 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 that kind of sets. This training will allow you to do more reps on a given percentage of your 1RM.
  2. Train to increase your maximum strength. Train with low reps and heavy weights, by, for example, adding extra weight in 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.

Simply put: 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

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:

Muscle Growth:

  • Anything between about 5–40 reps per set (between about 40–85% of 1RM) has been shown to give good muscle growth. 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. Here, the muscle-building effect is large, and it is quite easy to tire out your muscles.

Strength:

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

Note that these numbers apply to sets taken to, or close to (within a few reps of) failure. That is, the point where you no longer can do another rep.


More reading:

References

  1. European Journal of Sport Science, 22 March 2018. Effects of different intensities of resistance training with equated volume load on muscle strength and hypertrophy.
  2. J Sports Sci Med. 2016 Dec; 15(4): 715–722. Differential Effects of Heavy Versus Moderate Loads on Measures of Strength and Hypertrophy in Resistance-Trained Men.
  3. J Strength Cond Res. 2015 Oct;29(10):2954-63. Effects of Low- vs. High-Load Resistance Training on Muscle Strength and Hypertrophy in Well-Trained Men.
  4. J Strength Cond Res. 2017 Dec;31(12):3508-3523. doi: 10.1519/JSC.0000000000002200. Strength and Hypertrophy Adaptations Between Low- vs. High-Load Resistance Training: A Systematic Review and Meta-analysis.
  5. Front Physiol. 2018; 9: 402. Are the Hypertrophic Adaptations to High and Low-Load Resistance Training Muscle Fiber Type Specific?
  6. Int J Sports Med. 2016 Jun;37(6):442-7. Effects of Varied Versus Constant Loading Zones on Muscular Adaptations in Trained Men.

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