Effective repetition model: insufficient evidence


The idea that the last five reps before muscle failure are “effective reps” and are extremely important for muscle hypertrophy has no strong scientific support. In this article, I will go over the arguments behind the concept of “effective reps” and suggest another model that I hope will be better.

In 2016, I wrote an article “Is it possible to predict muscle growth?” … It ended like this: “You can say, ‘Damn it, man. Basically, you are saying that there is no reliable way to predict how much I will be able to pump up during training?”. My answer is yes, in fact. Of the available assessment methods, the most useful is tracking the number of heavy sets per muscle, followed by tracking the relative volume of the load. But these methods are rather approximate “… This answer did not suit everyone, because when developing a training program, people want to know what effects to expect from it, including quantitative ones. However, this is not about the fact that we do not even roughly know what will cause muscle growth: we simply cannot say what specific change in a specific program is guaranteed to give a group of people muscle gain by a specific percentage.

Over the past four years, the idea of ​​”effective reps” has gained popularity. It comes in several varieties. The most widely used one is by Chris Beardsley , although Borge Fagerli , James Krieger and Carl Juneau have also written about it . In short, the idea is that the last 5 reps before failure are “stimulating” because they are characterized by complete recruitment of motor units (MU) and a slow rate of contraction of muscle fibers (MV).

Chris Beardsley has written quite a lot about hypertrophy, and his understanding of the problem is much deeper than “the last 5 reps are important, and nothing else.” However, as often happens, a simplified version of his idea, voiced in a specific article  , has spread . Below is the same post by Chris.

 Strength volume is a key determinant of quantitative muscle growth. However, it is unclear how best to measure this volume. The most common methods are counting the number of sets to failure or determining the total amount of load (number of sets X number of repetitions X working weight). But they are not ideal because they do not accurately estimate the amount of mechanical stimulus that triggers muscle growth.

The mechanical stimulus that triggers muscle growth is the length of time during which the muscle fibers that make up the high-threshold MUs are activated and slowly contract. Contractions that occur at a faster rate or that do not involve the aforementioned fibers do not cause significant hypertrophy. Therefore, low to moderate intensity sets include a number of repetitions, which may not provide any stimulus for hypertrophy at all. Despite this, most modern methods of measuring the volume of the load take them into account as part of the total volume. It would be best to consider only those reps that activate high-threshold MUs and are characterized by low bar speed — and therefore stimulate muscle fiber growth.

I will try to refute this very simplified version. I am not refuting everything Chris has ever said on the subject, and I am not confusing his real beliefs with their popular simplistic version. I just want to show you that the idea that the last 5 reps before giving up is extremely important for hypertrophy doesn’t really have meaningful experimental support.

Effective Repetitions: An Overview of the Model Rationale

As far as I understand Chris’s logic, there are two main reasons to expect the last 5 reps before concentric failure to be really important for hypertrophy:

  • about 5 repetitions before failure, the DE is completely recruited;
  • shortly before failure, when the rate of muscle contraction is low, each recruited fiber experiences the greatest mechanical stress, due to which it receives a greater stimulus for growth.

I have come across two explanations for why almost all MUs are involved exactly 5 repetitions before failure. The first explanation comes from the classic work on isometric contractions . According to her, MU recruitment increases to about 85% of the level of the maximum voluntary force of contraction (that is, the level of one-repetition maximum, 1RM); the frequency of nerve impulses (determining the speed with which each MU is triggered) depends on the further increase in the effort after this point. It is also known that MU recruitment increases as fatigue develops and muscle failure approaches…. Since 85% of 1RM is approximately 5RM, it is believed that almost all MUs are engaged from the very first repetition with a load of 5RM or during the last five reps during a set to failure.

The second explanation is based on studies using electromyography (EMG), showing that the electrical activity of muscles, which depends on the number of recruited fibers and the frequency of their contractions, initially increases, but reaches a plateau about 3-5 repetitions before failure.

The significance of the low rate of contraction is justified by the well-known inverse relationship between the strength and the rate of muscle contraction. When muscle fibers contract concentrically at a high speed, they generate little force, when at a low speed they generate a lot. The fact is that the rate of connection of actin and myosin with the formation of transverse bridges is relatively low, and the rate of detachment of actin from myosin increases as the rate of muscle contraction increases…. This means that at a high rate of contraction, only a part of the potentially possible actin-myosin bridges can form, and therefore the voltage developed by the fiber is small. With a slow contraction, at any given time there are many more actin-myosin bridges, and therefore the tension developed by the muscle is much greater.

The idea that the degree of fiber recruitment and the high level of tension in each fiber are key to hypertrophy seems very reasonable.

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About the Author: Mildred White