Hypertrophy and VBT


Muscle mass is a determining factor in the production of strength in the various sports disciplines. In fact, increases in muscle mass are highly related to increases in force production. Once athletes become stronger they have greater potential to develop greater powers (1,2). However, the increase in this muscle mass should not follow the same direction as a program for a bodybuilder as it will probably end up ruining the athlete’s sporting performance due to the high levels of fatigue that can be reached. Furthermore, the improvement of strength may not achieve adequate development compared to other methods because levels of muscle strength are irrelevant to understand how muscle mass increases (4). Therefore, in this article I will explain the best strategies for increasing muscle mass through real examples with schemes that I usually use to achieve these objectives.

What physiological mechanisms are necessary to increase muscule mass?

There are mainly three, although not all of them are equally important:

  • Mechanical tension. This seems to be the most important factor in inducing increases in muscle mass and could be defined as the force that tries to stretch the muscle when it tries to contract. This mechanism has been shown to directly stimulate the mTOR metabolic pathway (3). Mechanoreceptors are sensitive both to the magnitude and type of contraction and to the duration (time under tension) of the loads (3).
  • Metabolic stress. Evidence has shown that it could have a less relevant role than mechanical stress. It is produced by the accumulation of metabolites after repeated muscular contractions.
  • Muscle damage. There is little evidence of this, and, in the case of sportsmen and women, there is little interest in generating high levels of muscular damage because of the impact that this would have on fatigue and performance.

Mechanical strain in Hypertrophy

When we lift a light weight at maximum speed, in spite of carrying a maximum intentionality, the mechanical tension experienced by the complex tendon muscle is low. This occurs because the strength that each muscle fibre is capable of exerting is low due to the short time taken to establish the cross bridges (4). However, when lifting this light load at a lower speed, the mechanical tension is even lower due to less motor recruitment.

Despite this, it must be understood that the mechanical tension experienced by the whole muscle is very different from the mechanical tension experienced by each muscle fibre (4). Although, the mechanical tension for the tendon muscle complex is low when a light weight is lifted with maximum intentionality, the motor recruitment is not complete, so the fibres that are activated can generate a very high force (4). This is the reason why, lifting light weights at low speed can generate less mechanical stress than at high speed.

With light weights, high volume is required, as engine recruitment will increase as the engine units are fatigued in order to maintain force production. When using a slow tempo, high threshold drive units will not activate until the end of the series and when recruited, they will experience high stresses. When a fast tempo is used, all types of motor units will activate during the series but will not reach high levels of mechanical stress until the speed decreases due to fatigue build-up and is similar to that which occurs when lifting high weights.

This means that muscular hypertrophy occurs when an individual muscle fibre experiences mechanical tension and not when the whole complex of tendon muscles does (4).

Despite all this, high strength (heavy loads) and fatigue imply high levels of motor recruitment at the same time, which is what stimulates the more responsive muscle fibres controlled by high threshold motor units and produces muscle growth (4). At low loads, even though high threshold motor units are recruited, they will hardly experience high tension.

Metabolic stress in Hypertrophy

First of all, we must differentiate between metabolic stress and fatigue. The latter occurs due to an inability to produce voluntary force and can occur due to peripheral phenomena through a reduction in the capacity of individual muscle fibres to produce force either due to a decrease in the release of calcium by the sarcoplasmic reticulum or a decrease in the sensitivity of actin and myosin myofilaments to calcium. And also, due to central mechanisms given by a reduction in the nerve signal sent by the central nervous system. Although it can also occur due to an increase in afferent feedback from receptors 3 and 4 (5).

Metabolic stress occurs due to the accumulation of metabolites and is thought to act by increasing muscle mass through

  • Increased motor recruitment:
  • Hormone release
  • Release of myokines
  • Release of reactive oxygen species
  • Cell swelling

However, the increase in motor recruitment does not occur mainly through the accumulation of metabolites but increases as fatigue increases. The role of myokines is not yet conclusive and the hormonal role due to post-exercise release is also contentious. Finally, cellular inflammation or swelling causes increases in pressure against the cell membrane generating increases in mechanical stress during active contractions (5).

Furthermore, studies investigating the role of blood flow restriction to the muscle (BFR) do not report evidence of increases in muscle mass when such accumulation occurs without muscle contraction.

For all these reasons, evidence suggests that mechanical strain may be the most important mechanism for increases in muscle mass.



Muscle damage in Hypertrophy

It has traditionally been believed that muscle growth occurs due to muscle damage. However, it should be noted that muscle growth and muscle repair are totally different processes despite the fact that both require an increase in myofibrillar protein synthesis (7)

In fact, muscle growth involves increasing the volume of the muscle fibre by increasing new myofibrils or increasing the length of existing myofibrils. On the other hand, muscle repair involves removing damaged areas of the muscle fibre and replacing it. When the muscle damage is very large, the old muscle fibre is completely eliminated and a new one is created within the existing cell membrane (7)

It appears that both increases in intracellular calcium and levels of inflammatory neutrophils in response to fatiguing contractions could degrade the interior of the muscle fibre (7). Reactive Oxygen Species (ROS) have also been shown to contribute to anabolism through the MAPK metabolic activation pathway. Since eccentric exercise is associated with increased MAPK activation compared to concentric and isometric actions, it is conceivable that ROS production contributes to this stimulus. ROS interferes with the signalling of several serine/threonine phosphatases, such as calcineurin (calcineurin is thought to be involved in muscle growth processes)

Exercise-induced muscle damage can contribute to the accumulation of muscle proteins. Although exercise-induced hypertrophy may apparently occur without significant damage, evidence suggests that microtrauma improves adaptive response, or at least initiates signalling pathways that mediate anabolism. Researchers suggest that macrophages play a key role in regenerative processes as they secrete local growth factors associated with inflammation processes. Despite this, a cause-and-effect relationship between muscle damage and hypertrophy has yet to be established. If this relationship exists, the degree of damage required to maximise muscle growth is not determined (3).

For all these reasons, it seems that muscle damage is an effect that occurs due to repeated muscle contraction and is not as decisive for muscle growth as is thought.

Why use clusters when it comes to hypertrophy in athletes?

In order for an athlete to obtain high performance in repeated power actions throughout a match, he must have

  • A high power output (6)
  • A capacity of resistance to power (6)


Accumulating large volumes of training while maintaining force production at high speeds during training can generate high power outputs and a high working capacity, improving not only the ability to recover between sets, but also increasing the quality of subsequent efforts and greater ability to recover between training sessions and matches (6)

Otherwise, including high volumes of training by means of traditional series will surely kill the strength production due to the high development of fatigue during and after the training reducing the performance during the following days. In fact, peak power is significantly higher during cluster series compared to traditional series (9, 10, 13, 14, 15, 16). In addition, they allow a greater volume of training to be accumulated, less time under tension, greater average power, an anabolic response similar to traditional series and less metabolic stress despite the training state (11). The time under tension increases with each series, but will always be greater with a configuration of traditional series (12, 16). In spite of this, the mechanical tension generated will be more than sufficient to generate increases in muscular mass and increase the levels of strength of the sportsman.

Is it necessary to reach muscle failure to achieve muscle mass gains?

It is hypothesised that around the last 5 repetitions a point of full motor recruitment is reached. In addition, near failure when contraction rates are slow due to fatigue, greater mechanical tension is produced.

However, expert athletes are able to recruit virtually all their motor units far from failure with multi-joint exercises. In fact, high-threshold motor neurons behave as follows:

  • MU 100: At 50% load they only reach ⅔ of their strength but at 80% load they reach their maximum strength and do so from the start (18).
  • MU 120: With a load of 50% they only reach ½ of their strength but with a load of 80% they reach ½ of their strength from the beginning (18).

In other words, all motor units are recruited but are only exposed to a fraction of their maximal force production from the first moment of contraction (away from failure).

In fact, if we review the literature we can find that training at or near failure produces greater increases in muscle mass (21, 22, 23, 26). On the other hand, we also found that stopping far from failure was clearly superior (19) and other studies yield data with no significant differences (25, 20, 24).

We have to take into account that 4 of the studies were carried out on trained subjects and with multi-joint exercises (26, 25, 22, 19) and the other 4 on untrained subjects and with isolated exercises (20, 21, 23, 24). When we analyse the studies carried out on trained subjects and multi-joint exercises, and perform a simple average of all the measurements taken of the muscle cross-section, we find that there is an 8.9% increase in muscle mass in sets further away from failure and a 9.2% increase in sets taken to muscle failure (27). These differences do not appear to be very large. However, in studies carried out on untrained subjects and isolated exercises, it seems that sets carried out at failure generate better results in terms of muscle mass gains. Therefore, the effective repetitions model may have greater application in isolated exercises.

Training to muscle failure in multi-joint exercises can generate high levels of fatigue and may not provide a benefit great enough to pay that price, at least in athletes.

It seems that the model of effective repetitions could be applied in reference to isolated exercises.

What percentage of velocity loss is optimal for increasing muscule mass gains?

Sets carried out at up to 40% loss of velocity generate greater muscle mass gains than sets carried out at up to 20% loss of velocity (22). In fact, sets ending at 20% loss of speed accumulate around 40% fewer repetitions. This extra training volume, accompanied by greater fatigue and greater mechanical stress due to greater motor recruitment could be responsible for these differences.

How can we apply this to our athletes?

A moderate volume, together with a good diet and rest, can certainly induce adaptations of hypertrophy in your sportspeople. However, sports such as football and rugby, where high levels of strength production and therefore muscle mass are required, may be interesting to include other types of strategies.

Furthermore, the hypertrophy generated by the use of cluster sets will be much lower than that generated by traditional sets, but the strength gains will be much greater. In fact, performing 5 repetition maximums may lead to greater gains in muscle mass than 5 singles due to greater time under tension, higher levels of mechanical load (28). With loads lower than 5Rm or 85% of 1 RM not all motor units are activated until you experience sufficient peripheral fatigue, so with lower loads it would be interesting to use longer cluster series (triples or doubles) and greater volume of the same.

In addition, if the situation allows luster series allow us to accumulate a greater volume of training with less fatigue (12, 16), so they are a good option when it comes to achieving this type of adaptation in sportsmen and women. In this way, despite programming high volumes of training, your athletes will be able to maintain this explosive capacity during the session. However, you will encounter the following limitations:

  • You will need a long time to complete the session.
  • Even if athletes are able to maintain their explosive ability during training, it is likely that muscle damage and high levels of fatigue will occur in the days that follow.
  • You will not achieve the same results as with a traditional program because, as we have seen, fatigue is necessary.


In spite of this, we can modify these guidelines to achieve a greater tonnage in the space of time available. So, I’m going to expose you the different schemes that I usually use to implement all this science in a practical way:

– Series of 3 triples @65-70% with 50” of rest (lower part) and 30-40” (upper part)imagen-4-carlos-vbt-encoder-vitruve-strength-training
– Series of 4-3 doubles @75% with 50” of rest (lower part) and 30-40” (upper part)

– Series of 8-10 singles @80% with 50” of rest (lower part) and 30-45” (upper part)

These 3 schemes require a long time to be carried out so if you have less time, you can use the following ones:

  • 8 series of 5 repetitions @70%.
  • 10 series of 3 repetitions @75%.
  • 12 series of 2 repetitions @80%.

These schemes require more rest time between series as the fatigue they will produce will be greater. Therefore the rest here can go from one minute to two minutes.



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3. Brad Schoenfeld. Science and development of muscle hypertrophy. 2ª. ed. Lehman College. 2017
4. Chris Beardsley. What determines mechanical tension during strength training?. Chris Beardsley. Nov, 14. 2018. Disponible en https://medium.com/@SandCResearch/what-determines-mechanical-tension-during-strength-training-acdf31b93e18
5. Chris Beardsley. Does metabolic stress cause muscle growth?. Chris Beardsley. Sep 13. 2018. Disponible en https://medium.com/@SandCResearch/does-metabolic-stress-cause-muscle-growth-f16acd4aff41
6. Jake Tuura. Hypertrophy Clusters Protocol Ebook.
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11. Oliver, J. M., Kreutzer, A., Jenke, S., Phillips, M. D., Mitchell, J. B., & Jones, M. T. (2015). Acute response to cluster sets in trained and untrained men. European Journal of Applied Physiology, 115(11), 2383-93.
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27. Max Schmarzo. The Evidence is Lacking for “Effective Reps”. Sep, 9. 2019. Disponible en https://www.strongerbyscience.com/effective-reps/
28. Chris Beardsley. How does proximity to failure affects hypertrophy. Feb 14, 2019.

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