Effective reps: fact or myth?

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There is a lot of debate these days in the evidence-based bodybuilding community about effective reps. More and more coaches are embracing the theory that only the last five or so reps of a set, just before muscle failure, cause muscle growth. So we call these effective, or stimulating repetitions. But there are also critical comments on this (plausible) theory.

Key points:

1.   The reps in a set will provide more growth stimulus the closer you get to muscle failure. To achieve muscle growth, you will therefore have to make sufficient effort during your sets. Still, it’s not necessarily the last five reps before muscle failure that drive the most muscle gains (the “effective reps”), as a popular theory dictates.

2.   The last two repetitions immediately before muscle failure (2-0 RIR) and muscle failure itself (-1 RIR) have an unfavorable Stimulus:Fatigue Ratio. (A lot of) training until muscle failure is therefore at the expense of your recoverable volume, so that you can do fewer sets and therefore on balance less effective reps. It is therefore best to train your sets to about 2 RIR, unless a deload is imminent.

3.   It is also not necessarily only the repetitions from 5 RIR that have an effect. Particularly with large, compound exercises, the ‘early’ repetitions in a set also provide some growth stimulus. That’s why you can safely stay a little further away from muscle failure with these types of sets, for example 3 RIR. Training status may also play a role: advanced bodybuilders probably need less far to muscle failure for maximum muscle growth than beginners.

4.   Because the repetitions in a set do not all produce the same stimulus, it is difficult to calculate them as training volume. That is why you can best express training volume in hard sets, where those sets must meet fixed criteria, like doing 6-20 repetitions at ~2 RIR.


The idea of ​​the stimulating repetitions is certainly not new. As Arnold Schwarzenegger once said:

The last three or four reps is what makes the muscles grow.

Now that statement comes from the era when bodybuilding was still mainly a matter of intuitive training. But a few decades later, it received acclaim from science. We now know that you can achieve maximum muscle growth with both light and heavy weights, as long as you train until (near) muscle failure. Only with light weights you simply need more repetitions to achieve the growth stimulus.

This growth stimulus is caused by the muscle becoming fatigued during a set. And fatigue (in the muscle) leads to slow muscle contractions, activating the large motor units in the muscle, the motor units that provide the most mechanical tension and thus the greatest growth stimulus. Mechanical tension is therefore not so much determined by the absolute weight you use, as it turns out, but by the activation of muscle fibers and the speed at which that happens.

We illustrate all this once again with the image below, which aptly depicts the principle of effective repetitions. The red colored reps can be regarded as the effective ones.

It’s about the reps that feel the heaviest, regardless of the weight and number of reps you use in a set. (Source: YouTube/Radu Antoniu )

For practical reasons, it is best to train in the range of 6 to 20 repetitions. If you do fewer repetitions, you may miss some ‘red’ and therefore effective repetitions. For example, in a set of two, you would have only two effective reps, as shown in the image below. If you do more than 20, central fatigue starts to play a role and you may be stranded with your set well before muscle failure. Then, according to the theory, you would have done a completely pointless set – see figure below. In this case we ignore the assumption that long sets create a lot of metabolic stress and that in itself can also cause muscle growth.

According to the theory of effective reps, only the last five reps of a set are important for muscle growth, assuming you train the set to muscle failure. (Source: YouTube/Jeff Nippard )

The theory of effective repetitions was elaborated and popularized by researcher and author Chris Beardsley, most notably in a 2018 article.


To properly understand the theory, it is important that you are familiar with the term Reps In Reserve (RIR).

The greater your effort, the greater the relative intensity (or intensity of effort), the more effective reps. We usually express this relative intensity in Reps In Reserve (RIR). 5 RIR means you could have done five more complete reps at the end of the set. 1 RIR means leaving your set ‘in the tank’ for one rep, i.e. stopping one rep before muscle failure. At 0 RIR you train to muscle failure and at -1 RIR to absolute muscle failure (you fail in the concentric phase of the exercise).


If you train a set to near muscle failure, for example with 2 RIR, it will probably yield four to five effective repetitions, according to the theory. Nice, but that’s not enough to grow a muscle. According to Beardsley, for maximum muscle growth, an average bodybuilder needs about 75 effective reps per muscle group per week, assuming an even distribution over three weekly sessions with 25 effective reps each. To reach that number, you will have to do several sets for each muscle group. Assuming 5 effective reps, that means an average bodybuilder should do about 15 sets per week, with a maximum of 5 sets per muscle group per session.

Beardsley’s calculation is based on sets that are trained to complete muscle failure. If you leave some reps in the tank, you can do 5-12 sets of maximum productive volume per workout.

You create a growth stimulus by doing enough sets and by making sufficient effort per set, so by training until (near) muscle failure.


For the past weeks, effective reps have been a hot topic within the evidence-based bodybuilding community. YouTube coach Jeff Nippard devoted a video to it, coach and scientist Mike Israetel had his say on a Revive Stronger podcast, and his colleague Greg Nuckols published an awesome article on Stronger by Science.

Where Israetel introduces the necessary nuances to the concept of effective repetitions, Nuckols even dares to question the whole concept. The latter dug up a lot of scientific studies and came to the conclusion that the evidence for effective reps is thin and you should at least make some caveats.

While Nuckols recognizes that optimal muscle growth requires training somewhat close to muscle failure: if you can do 12 reps with a weight, 3 sets of 10 reps are almost guaranteed to achieve more muscle gains than 3 sets of 3 reps. But it’s too simple to say that the last five reps of a set are the most effective. Moreover, the number five is not based on anything, and is probably only used by Chris Beardsley to simplify and clarify his theory.

Below we summarize the main nuances and reservations about the theory of effective repetition, as expressed by Nuckols and Israetel.


The theory of effective reps suggests that you need to go all the way with each set to get as many fatiguing, stimulating reps as possible. Because looking purely at stimulus, you can say that you achieve the most growth stimulus and therefore also the most muscle growth if you train completely to muscle failure.

However, several studies have now made it plausible that it is better to stay away from muscle failure. The main reason for this is the Stimulus:Fatigue Ratio (SFR), or the amount of fatigue that is opposed to a certain growth stimulus. The more fatigue, the more is required of your recovery capacity.

Mike Israetel explains in the Revive Stronger podcast that the roughly five repetitions immediately before muscle failure do not all trigger the same growth stimulus and are therefore not all equally effective. From about 5 RIR there is an S-curve, as shown in the figure below.

Initially, there is a strong growth stimulus, so it makes quite a difference whether you train with 5 RIR or 4 RIR. But the growth stimulus quickly flattens out. As a result, it makes almost no difference whether you train with 2 RIR, 1 RIR or 0 RIR. Something that is confirmed by a recent study by Carroll et al. However, at 0 RIR you have still created the largest stimulus in total and, in theory, also achieved the most muscle growth.

From 2 RIR onwards, the stimulus of the repetitions decreases. As a result, from 2 RIR to muscle failure, you will not achieve much extra muscle growth. (Source: YouTube/Jeff Nippard )

We say “in theory” because one usually doesn’t do only one set and any stimulus is accompanied by tiredness (fatigue). And it’s those last two reps (0-1 RIR) that cause by far the greatest fatigue. And just as the extra stimulus in the last two reps is relatively small, the extra fatigue is relatively large. In short, an unfavorable SFR is created, as you can see in the figure below.

You achieve the best Stimulus:Fatigue Ratio (SFR) by training about two repetitions of muscle failure (2 RIR). (Source: Mike Israetel/Renaissance Periodization )

That SFR seriously comes at the expense of your recovery capacity and therefore of the total productive training volume you can do. And less volume means less muscle growth. That is why most reputable coaches nowadays recommend that you usually train with 2 RIR (except possibly in the week prior to a deload). That means you’re essentially throwing out two effective reps on each set. But you do that to be able to do more volume in total and therefore more effective reps.

Greg Nuckols sums it up like this:

(…) More tension promotes more hypertrophy up to a certain level, but you don’t need maximum tension on each fiber to maximize hypertrophy. And more fatigue promotes more hypertrophy up to a certain level, but you don’t need maximum fatigue to maximize hypertrophy.

The foregoing does not essentially undermine the theory of effective repetitions. It does mean that it is not so much the last five repetitions of a set that are important, but the repetitions between say 6 RIR and 1 RIR.


It’s too bold to say that only the last few reps of a set are effective. Also the repetitions before your 5 RIR have – to a certain extent – ​​a certain effect on hypertrophy.

Exactly how big depends on the weight you use. If you use a heavy weight with which you can only complete eight repetitions, it is likely that you will already receive some stimulus from rep one. If you use a light weight with which you can do twenty reps, then something of a stimulus will only start to arise from about the twelfth rep. However, most bodybuilders train in the range of 6 to 20 reps.

So it is too simplistic to count only effective repetitions for training volume, as some do. It is best to express training volume in hard sets, regardless of the number of repetitions, as long as it is within the range of 6-20 repetitions and with an efficient relative intensity (~2 RIR).


According to Nuckols, you can’t just apply the principle of effective repetitions to everything. For example, there is a difference between compound exercises (multi-joint) and isolation exercises (single-joint).

Research suggests that with multi-joint you engage all motor units in a muscle faster than with single-joint, at least as far as the target muscle of the exercise is concerned (for example, the chest when doing a bench press). Nuckols doubts whether the tension experienced by individual muscle fibers is the only indicator of muscle growth. The proteins responsible for that muscle growth are located around the attachment points between the muscle fibers and the connective tissues that pull on the muscle fibers. And those connective tissues play a much greater role in compound exercises than in isolation exercises, so that the individual muscle fibers may experience optimal tension more quickly.

So you probably don’t have to train as far to muscle failure for maximum muscle growth with compound exercises as with isolating. In other words: with compound exercises, repetitions are more effective than with isolating.


According to Nuckols, it also makes a difference whether you are a beginner or advanced. Advanced users usually use heavy weights and the body adapts to them by improving the synchronization of motor units. To put it more simply, it can activate more motor units at once, allowing the muscle to produce more force. That pretty much happens in the first repetition of a set. As a result, reps further from muscle failure are likely to be more effective in advanced bodybuilders than in beginners. Beginners are, incidentally, more sensitive to training stimuli, which is why they may also be able to achieve muscle growth with lighter repetitions, but that aside.

However, the foregoing is mainly the case with compound exercises (see also point 4), where heavy weights are usually used. For example, Nuckols found four studies conducted on experienced strength athletes. Compound exercises were used in all four and in all four there was no significant difference in muscle growth between training short for muscle failure and staying further away. Nuckols also found four studies conducted on novice strength athletes who performed isolation exercises. It turned out that training shortly to muscle failure resulted in an average of almost twice as much muscle growth as staying a little further away!


It’s true that reps in a set provide more growth stimulus the closer you get to muscle failure. To achieve muscle growth, you will therefore have to make sufficient effort during your sets. Quitting a set when you could have done more than five reps is pointless. However, that does not mean that by definition only the last five repetitions are effective.

In the first place, the one or two repetitions immediately before muscle failure (2-0 RIR) and the moment of muscle failure itself have relatively little added value in terms of stimulus compared to the repetitions before that (5-2 RIR). This while they cause relatively much fatigue. This creates an unfavorable Stimulus:Fatigue Ratio, which is why it is best to keep these repetitions in the tank. It is therefore better not to train your most sets completely to muscle failure, but to end at 2 RIR.

Secondly, it is not necessarily only the repetitions from 5 RIR that have an effect. If you do compound exercises, the reps before 5 RIR will also engage many motor units in your muscles. The ‘early’ repetitions of your set also provide some growth stimulus. That is why you don’t have to train such a set as far until muscle failure and you can suffice with 3 or 4 RIR, for example. Sets of isolating exercises, on the other hand, must be trained close to muscle failure to create sufficient stimulus.

Thirdly, training status may also play a role: advanced players probably need less far to muscle failure for maximum muscle growth than beginners.

Because the repetitions in a set do not all create the same stimulus, it is difficult to calculate them as training volume. That is why you can best express training volume in hard sets, where those sets must meet fixed criteria. Usually it is based on sets of 6-20 repetitions and an average of ~2 RIR.


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