What Science Has to Say About Building Muscle

Here’s how you can use research to guide your lifting life.

Science is a way of developing knowledge; a mechanism to establish what you accept as sufficiently “real” to allow you to act upon, and thereby live your life. So, science can help guide how you live your lifting life.

Scientific research consists of systematic observation, measurement, and experimentation. In theory, science should be perfect. It should provide the exact answer to our specific questions. It should provide the truth. However, as Bret Contreras points out, “humans are inherently flawed…we inevitably muck up the flow of science.”

This is one reason why not everything you see on PubMed should be taken as gospel. When it comes to hypertrophy, there is another caveat: helping gym junkies build obscene amounts of muscle is not a priority for most researchers, or those who fund their studies.

As such, much of the research is focused on preventing or treating diseases or medical conditions. Consequently, extrapolating useable conclusions from this research and applying it to the healthy meathead is problematic.

Do You Even Science, Bro?

This does not mean that you should ignore the available science. Far from it. You should embrace it, but with a cautious and logical mindset. Rather than looking at what one rogue study says and drastically changing your training based on that, it is best to look at the weight of evidence across the whole catalogue of available literature.

By doing so, you give yourself the best chance of making well grounded, scientifically backed, evidence-based decisions about your training. Decisions based on that thought process will lead you towards training that is optimal.

Recently, there has been a lot more research on the mechanisms and training principles of hypertrophy. This makes recommendations for training for hypertrophy, based on science a lot easier than it was just a few years go.

Do yourself a favor, and brush up on what science can teach you about hypertrophy. Haven’t got time to read a ton of journal articles? Don’t worry, I’ve done it for you, and I’ve sifted through the research to provide you with the key takeaways.

This article covers all the key training variables, such as intensity, volume, and frequency. I’ll analyze if you need to train to failure, tell you how long you should rest between sets, and explain how you should order exercises.

I also discuss whether you need to use a full range of motion, and if tempo training is all it’s cracked up to be. Read on to learn more, and follow these guidelines to grow as fast as humanly possible!


Intensity is defined as the percentage of 1-rep max (1RM) used when performing an exercise.

Most sports science textbooks refer to three different bands of relative intensity when discussing resistance training. These are typically described as heavy (1-5RM), moderate (6-15RM) and light (15RM+). These are also widely known in gyms as the strength, hypertrophy and strength endurance rep ranges.

These divisions between heavy, moderate and light loads are somewhat arbitrary, and should not be treated as hard and fast dividing lines.

The research on intensity is somewhat contradictory, and the lack of agreement between studies makes a definitive answer difficult. Significant hypertrophy can occur across the whole spectrum of intensity.

However, the weight of evidence suggests that the use of heavy loads (i.e. >65% of 1RM) is superior to the use of lighter loads (<65% of 1RM) for producing hypertrophy. This is especially the case once you have passed the beginner stage.

Mathias Wernbom’s meta-analysis showed a tendency for rates of muscle size increases to peak at around 75% of 1RM, and the results of his review support the traditional recommendations of training in the medium rep range for hypertrophy.

Training in this range is likely optimal because:

“Training in the medium rep range gives the optimal combination of mechanical tension and metabolic stress for maximizing hypertrophic adaptations. Loads are heavy enough to recruit the majority of fibers and to maintain their stimulation over a sufficient period of time. Moreover, sets generally last 20-40s, requiring a substantial contribution from fast glycolysis and correspondingly generating high levels of metabolic stress.”

Brad Schoenfeld

Wernborn’s review, however, stated that there is a remarkably wide range of intensities that may produce hypertrophy. Thus, it appears that spending most of your training time in the medium rep range is best suited to increases in muscle size.

With that said, spending some time in other ranges is likely beneficial to maximizing hypertrophy. Training through a wide spectrum of rep ranges allows all avenues for the hypertrophy to be exploited.


Training volume is your total workload per exercise, session and week. A simple way to track it is the following equation:

Sets x Reps x Load

It is well established that using multiple sets is superior to using single sets to achieve hypertrophy. This is explained by the ability to achieve a higher volume of training.

The literature provides compelling evidence that higher training volumes are necessary to maximize anabolism. In fact, assuming the previously mentioned intensity threshold of >65% is met, it appears that volume is the key determinant of success when it comes to gaining muscle mass, and that above this threshold, volume is a better predictor of hypertrophy.

A dose-response relationship exists between training volume and hypertrophy, until a point at which you overtrain. The relationship between volume and hypertrophy is hypothesized to follow an inverted-U curve. Muscle size increases peak at a given volume load, and beyond this point, further increases in volume impair muscular gains.

An excellent example of this is the systematic review by Wernbom and colleagues. This showed that the cross-sectional area of the elbow flexors increased from 0.15% per day when 7-38 repetitions were performed per session, to 0.26% per day when 42-66 repetitions were performed per session. This rate of increase then declined to 0.18% per day with volumes in the 74 to 120 repetitions range.

This indicates that there may be a ‘sweet spot’ for training, at least in the elbow flexors, where maximal increases in size occur. Once this threshold is crossed, it appears a transient overtrained state is reached that impairs hypertrophy. The review established that 4-6 total sets cause optimal hypertrophy in the elbow flexors.

All of this means that you most likely do not need a whole training day dedicated to arms, and doing more than six sets for more than 74 total reps per session might impede the rate of your muscular gains. Wernborn’s meta-analysis identified that the highest rates of hypertrophy tend to occur with 30-60 repetitions per session for most muscle groups.

The law of diminishing returns applies to hypertrophy training. This states that the more you do something, the less return you get. In the case of hypertrophy training, it seems that the first set is the most important, and each subsequent set provides a reduced stimulus.


Traditionally, frequency has been associated with how many days a week you train. When it comes to hypertrophy, the number of times a given muscle group is trained per week is probably a more important consideration.

Superior results across a wide range of indicators (strength, increases in lean body mass, neuromuscular adaptations, and hormone markers of recovery) result from volume-equated, high-frequency programs with less volume per session.

Splitting the same training volume into more frequent training sessions is superior for hypertrophy. This is likely because the hypertrophic stimuli are distributed more optimally over the course of the week in higher frequency training approaches.

Training a muscle group twice a week is better than once per week. Novice lifters may benefit from training a muscle group more frequently (up to 4 days per week), than intermediate or advanced trainees. More experienced lifters seem to achieve optimal rates of progress in muscle size with a weekly frequency of 2-3 days per week.

While training more often than once per week is superior for advanced lifters, it is not clear whether training a muscle more often than twice per week for experienced trainees is better for muscle growth.

As a result, we can conclude (for now) that training a muscle twice a week is suitable for optimizing hypertrophy. It is possible that a higher training frequency may be superior (at least in some muscle groups).

Decades of anecdotal evidence suggests that certain muscle groups can be trained more frequently than others.

For example, the rear deltoids and calves have often been trained 4+ times a week by bodybuilders with excellent results. On the other hand, it is extremely rare for the quadriceps to be trained in this manner. As of yet, there is not sufficient scientific evidence to provide individual muscle-specific frequency guidelines.

It seems that a tentative recommendation for training smaller muscle groups more frequently than larger ones is likely to be effective. We must wait for further research to be conducted before this can be assessed scientifically.

It worth remembering that frequency should not be considered a set-in-stone variable. While it is highly likely that long-term, high frequency training could lead to overtraining and injury, short-term, very high frequency training can serve a purpose.

This is especially the case in phases of functional overreaching. Thus, it would likely be wise be to default to frequencies of 2-3 times per week, with periods of more frequent training (i.e. 4+ times a week) strategically and sparingly used.

Training to Failure

Training to failure is one of the most contentious topics in bodybuilding. Despite the great debate in gyms worldwide on this subject, little research has been conducted to investigate the issue.

Given the lack of research, it is difficult to give a definitive answer to the question of whether to train to failure or not. Beginners seem to be able to gain strength and hypertrophy without reaching failure.

There does, however, appear to be an increase in hypertrophy when training to failure in comparison with not training to failure, when other variables are equated. Although a recent study reported similar hypertrophy when training to failure or stopping just short of failure.

It appears that training to, or very close to failure is more important when training with lower loads (<60%). Research indicates that muscle protein synthesis (MPS) is blunted if sets are not taken close to failure with low loads.

Furthermore, training to failure at low loads resulted in MPS being elevated more than when taking a heavy load (90%) to failure. Consequently, your proximity to failure should probably increase as the load gets lighter.

Training to failure increases muscle activation, but has been shown to decrease volume on subsequent sets for the muscle group. In fact, this led the researcher Mikel Izquierdo to describe training to failure as a “disproportionate stress to stimulus.”

Anecdotally, training to failure is widely acknowledged to be very demanding upon the recovery capacity of an individual. Given that the research to date is all short-term in nature, it is best to exercise caution when training to failure. It is not required to train to failure to cause hypertrophy, but there is limited evidence that occasionally incorporating it might lead to superior gains in hypertrophy.

Rest Periods

It has long been considered that training with relatively high reps and shorter rest periods is optimal for hypertrophy.

The research does not fully support this, though. In fact, studies comparing short and long rest periods have reported conflicting results with respect to hypertrophy.

One of the problems with drawing conclusions from this research is that training volume was not always equated, and the groups that used shorter rest periods often trained with lower volume. Unsurprisingly, the lower volume groups saw less hypertrophy.

This perhaps indicates that rest period length is of little importance to hypertrophy, if training volume is maintained. As such, a practical guideline is to not use rest periods so short that they compromise the overall training volume of a session.

From a practical standpoint, it is wise to take longer rest periods following maximal effort sets (e.g., sets taken to failure or close to 100% of 1RM). According to Mathias Wernbom:

“It appears that when maximal or near-maximal efforts are used, it is advantageous to use long periods of rest…when using submaximal resistance, the size principle dictates that motor unit recruitment and firing rates are probably far from maximal until the muscle is near fatigue, or unless the repetitions are performed with the intention to execute the movement very quickly.”

Exercise Order

Generally, it is advised that multi-joint exercises are done at the beginning of a training session. Exercises that use the most muscle mass and require the most coordination should be done first. With regards to hypertrophy, the research indicates that this is not necessarily required.

According to the literature to date, it appears that you should order exercises based on your current strengths and weaknesses, which muscle group you are prioritizing that day, and how important the exercises are to you and your goals. The most important exercise(s) should be done first in the session.

Consequently, larger muscle groups don’t have to be trained before smaller ones. For example, you might choose to target smaller muscle groups first, if their development is lagging. Trainees get superior results for the exercises which are done early in a session.

Range of Motion (ROM)

Instinct probably tells you that a greater range of motion equates to greater gains in hypertrophy. Until recently, however, research had not been conducted to demonstrate this.

Perhaps because everyone was so certain that it was true it was not perceived as useful research. Anyway, some research has now been conducted, and multiple studies have established that increased hypertrophy occurs when the full ROM is used.

While the research in this area is very limited, the current evidence suggests greater ROM leads to greater hypertrophy. As a result, using a full ROM should be your default setting.

Partial reps can still can be used to target specific muscles. For example, performing the top half of a bench press to focus the overload on the triceps, or rack deadlifts to target the spinal erectors.


The speed at which you perform a lift is a variable which many believe to influence hypertrophy. Largely, this discussion centers on the hypothesis that by slowing down reps, you increase ‘time-under-tension’ (TUT). It has been claimed that greater TUT leads to increased hypertrophy.

Only a limited number studies have investigated the effects of repetition speed on hypertrophy. Of these, only one found a significant effect of rep speed on hypertrophy.

Perhaps surprisingly, that study reported that a fast rep speed was superior for hypertrophy than a slow rep speed. This study was conducted in elderly males, so it is hard to extrapolate these findings to the younger population of regular gym goers.

The other studies have shown non-significant and conflicting findings, making a definitive statement on tempo’s effect on hypertrophy extremely difficult.

It appears that, if there is any effect of rep speed on hypertrophy, it is marginal, and that lowering weights under control and lifting explosively will most likely have the most favorable effect on hypertrophy.

The Scientific Guidelines for Hypertrophy

The above scientific research can be condensed down to the following guidelines:

  • Lift loads heavier than 65% 1RM most of the time
  • Do 40-70 reps/muscle group/session, for a total of 80-210 reps/muscle group/week
  • Train each muscle group 2-3x per week
  • 66-75% of your sets should be in the 6-12 rep range
  • Most of those should be for sets of 8-10, close to, or to failure
  • If performing sets lighter than 60% 1RM, go to failure
  • Rest sufficiently long so as not to compromise overall training volume
  • Train whatever exercises are of highest priority to you first
  • Using a full ROM should be your default setting
  • Lift with a moderate tempo (about a 2 second eccentric and 1 second concentric)

I’ve done the research for you, and given you an overview of what the world’s leading researchers have to say on training for hypertrophy.

Now you just need to get in the gym and follow the experts’ advice to build a ton of muscle. What are you waiting for? Get growing!

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