Training for Hypertrophy: The Function of Intensity, Volume, Recovery and Injury Prevention

Here is an article i wrote for another forum. @Andrewgen_Receptors suggested that this would be helpful to the community here as well.

There has been a lot of debate on the subject of Hypertrophy in regards to training to failure, reps in reserve methodologies, volume, and injury risk. From what ive witnessed is a lot of this stems from a simple misunderstand on what these terms actually mean in most cases, a simply outdated view on the topic, or an unawareness/misunderstanding of the current body of literature we have on these topics.

In this article I aim to outline and define these terms for the communities greater understanding, give an overview of the most current literature we have as it pertains to these topics, and dispel some of the deep rooted, for lack of a better word, broscience surrounding these topics leftover from an era where we did not have access to the level of information that we do today.

Additionally I will be outlining what these terms mean to you, the lifter with the goal of hypertrophy, and how they all fit together for you to make the most out of your training.

Who am I?

A lot of you already know me, but for those that dont, and for those that stumble across this article later, I’m Tom.

I am, at the time of this article, 30 years old, 6’ tall, and 240lbs, and my best in competition lifts in the 110kg raw category are: 255/180/300kg or 561/396/661lbs.

I am a competitive classic physique and heavyweight bodybuilder, competitive power lifter, and coach with over a decade of training experience. On top of that I am a tremendous nerd that has spent countless hours researching all things bodybuilding and strength sports, and I’m learning more every day.

While this article will mostly be targeted for a bodybuilding context, there is a heavy overlap into strength sports and powerlifting.

For starters we will define the various terms in the topic of this article.

What is hypertrophy?

Hypertrophy is the process by which we increase the SIZE of muscle fibers within a muscle group.

This is accomplished through the application of mechanical tension. Mechanical tension is a term to describe load, over time, placed upon a muscle through a targeted range of motion. The more common term, time under tension, can also be used to describe mechanical tension. It is, in essence the stimulus required to drive adaptation. Through this adaptation, an increase in the size of the muscle cells occurs, this is Hypertrophy and is the primary goal of bodybuilders, and most gym goers.

Within a given set, of any given load, the last 5 repetitions before failure stimulate the most hypertrophic response, while the reps prior to 5 RIR providing very little hypertrophic response.

What is Training to Failure?

Training to failure is exactly as it sounds, taking a particular set until you cannot perform another rep, through the full range of motion, with good form.

Based on the most recent data available training to failure (sometimes expressed as RIR-0(zero reps in reserve), or RPE10 (rate of perceived exertion 10/10) produces the absolute most hypertrophy in a given set, furthermore there are two types of failure; Positive failure, which is the point at which you cannot complete another repetition in the full range of motion without compromising form. and Absolute Failure, which is the point that under no circumstances can the muscle perform another complete repetition, regardless of form compromise.

Training “beyond failure” is a disingenuous term and inaccurate, training beyond failure in an absolute sense, is impossible.

“Training beyond failure” through the use of drop sets, forced reps, spotter assistance, and other intensifier techniques do not actually progress you beyond failure in an absolute sense, but only allow you to get close and closer to true failure.

For example, lets say you are performing an incline dumbbell press, you fail at 8 completed reps, but are able to push halfway to the 9th rep before you lose stability and cannot complete the rep, this is positive failure. If you utilize a spotter to aid you in getting that 9th rep, and aid you even more for a 10th rep, you have used intensifier techniques to get closer to true failure. You are no longer capable of providing enough force to complete that rep alone with that weight, so the use of a spotter takes some of that load to allow you to progress through the complete range of motion, getting you closer to actual failure.

What is intensity?

Intensity can be defined as “proximity to failure”. Intensity is NOT fatigue, it is NOT feeling completely wiped out at the end of a set or workout, intensity is NOT going balls to the wall on some crazy super set or drop set, intensity is NOT heavy weight low reps. Intensity ONLY refers to proximity to failure in a training context. Intensity can be expressed with any weight, in any rep range.

Intensifier techniques (drop sets, forced reps, partials, ect) are tools used to get us closer and closer to true mechanical failure.

What is volume?

Volume can be separated into two categories, working volume and junk volume.

Working volume, is the number of working, adaptation driving sets for a given muscle group in a given session. Junk volume is any non-warmup, non-workup set, a set which does not stimulate a significant hypertrophic response. Examples of junk volume would be; pump sets, any set not taken to proximity of failure, supersets of more than one muscle group which neither is taken to proximity to failure (super setting leg extensions and leg curls with neither taken close to failure). These are referred to as junk volume, because they provide little to no hypertrophic response or adaptation and only contribute to fatigue and injury risk. In other words, they are worthless and counterproductive for building muscle.

Volume, when referring to rep ranges in a single set, is Set Volume. For the purposes of this article, and when discussing the topic of intensity vs volume in general, “volume” is referring to number of working sets.

What is recovery?

Recovery is the rate by which you can regain full capability in a muscle group after training. Additional fatigue from either intensity or volume increase recovery time. Recovery can be defined, for our applications, as “The time it takes after a session, to be able to train that muscle group again at the same or greater performance”.

The absolute best way to gauge recovery is through performance and progressive overload, if you are coming into your leg days and consistently performing less than the prior week, recovery is the culprit. Conversely, if you are feeling good and progressing consistently on a given training day, your recovery is great.

In order to maximize our training blocks, we need to minimize the time we spend fully recovered in between sessions, If you are recovering several days before your next session, than you have a lot of room in your training to either add volume (as defined here) or frequency.

It is generally better to increase individual training session volume (more working sets) to achieve Maximum Recoverable Volume (MRV), given that you are capable of adding more productive working sets to your session. If a single session is too fatiguing to add additional meaningful volume, then rather than falling into a hole of adding useless junk volume, it is better to increase frequency (reduce the number of days between training sessions for that muscle group

How they all work together

Now that these terms have been fully defined and explained we can move on to how these pieces fit together.

Hypertrophy is a function of intensity and volume limited only by recovery.

As ive discussed, training intensity on working sets should be a constant IE you should be training to failure or at least in very close proximity to failure.

If we think of this function like an equation is would look something like Intensity * Volume / Recovery. If we consider intensity as a prerequisite and a constant, that leaves volume and recovery as our working variables. Additionally we can assume recovery is a constant or at least relatively constant, given proper recovery practices (nutrition, supplementation, sleep, PEDS, stress management, ect).

So now that we have two relative constants that shouldn’t change much week to week, our only variable remaining is volume.

If you want the most out of your training the goal now is to achieve MRV. We achieve this by titrating up and down working volume such that we are getting the most work in, but still recovering.

How to leverage your recovery periods to get the most out of your split

As ive touched on already, if we want to make the most out of our training week or block, we need to properly manage recovery periods such that we are fully recovering by the next time we hit a specific muscle group, but not spending copious time fully recovered, we grow as we recover, so any time not spent recovering is time spent not growing.

To minimize the time spent fully recovered we have two options, 1) increase working single session volume, or 2) increase our frequency. Both are effective options and one may be more favorable depending on the number of training days you have in a block, length of your training block, and individual work capacity.

If you are someone who leaves the gym after a session with no gas left in the tank, meaning it would be exceptionally fatiguing and near impossible to add more single session working volume to your training session, or if you are someone whos training is time limited, increasing frequency is your best option to minimize that amount of time spent fully recovered.

Conversely if the opposite is true, and you typically leave the gym with some work capacity remaining, and do not have a time constraint, adding a few more working sets is a great way to make the most out of your recovery periods.

What about injury risk?

A very common misconception is that training at a high level of intensity poses a greater risk of injury. This belief system is largely due to the misconception that high intensity training requires higher working loads in lower rep ranges. As stated earlier in this article, this is not the case, training with a proper level of intensity and even training to positive failure can be accomplished with any weight in any rep range between 5 and 30 reps.

There is currently ZERO evidence that training to failure intelligently poses any greater risk of injury, in fact the opposite is true. Higher volume training and higher repetition movements are a large contributor to systemic fatigue and common injuries such as tendonitis. Assuming proper form is maintained, proper load selection, and proper management of recovery periods, you are at absolutely zero additional risk of injury by training to failure than not.

Should we train to failure?

Based on our current understanding of the literature available, if you want to make the most progress out of your training, the answer is an undeniable “Yes”.

It is currently suggested by the literature that hypertrophic response increases proportionally (and in some studies increasingly) with proximity to failure, with the majority of this response occurring between 5-0 reps from failure (some studies suggest 7-0). It has been shown time and time again that individuals grossly underestimate their RIR and are incapable of judging failure, without reaching it. Even for the most experienced individuals, whom train to failure regularly, consistently underestimate how many RIR they have. While training a rep or two away from failure has been shown to be effective at driving hypertrophy, consistently and accurately estimating a rep or two shy is a near impossibility.

For this reason, you, as a serious lifter, should be take at least some of your sets to failure.

You are at no greater injury risk, and while training to failure is exceptionally fatiguing, with proper rest intervals between sets, the overall session fatigue will be less than if you made up those reps with additional volume, which is far more fatiguing.

For example lets take two options for a particular movement.

3 sets of 10 to failure, yielding 15 total hypertrophy stimulating reps


5 sets of 10 with 2 reps in reserve, also yielding 15 total hypertrophy stimulating reps

Even assuming you estimated your RIR perfectly (which you almost certainly didnt) the 5 set option would be more fatiguing for almost everyone.

A Note on Effective Reps

As discussed in this article, we touched on how the last few reps before failure are the most effective
and driving hypertrophy according to the current literature.
BigBaldBeardGuy has provided a great breakdown on force production and why this is the case

The concept of “effective reps” and why they work so much better than the other reps is because when you get closer to failure, the speed of the reps always slows.

With force of a movement measured as:
Force = mass x acceleration

The mass is constant and since acceleration slows close to failure your muscle fibers must produce more force which results in the tremendous amount of mechanical tension on the muscle fibers. You don’t see that at all and there is very little mechanical tension in the easy reps. You can curl a barbell 100 times and it moves fast and easy during the early reps. But eventually the barbell starts to slow and gets slowest in proximity to failure. That’s when you can feel the mechanical tension and those are the effective reps. The reps that maximize the number and recruitment of muscle fibers, which leads to the hypertrophic response. Stoping short of that simply because your program arbitrarily indicated “20-25 reps” stops well short of the effective rep range. The workout does nothing for muscle growth.

A note on motor unit recruitment and neurology.
BRICKS provided some very useful insight and additional context on the subject of neurology and motor recruitment.

Muscle fibers contract all or nothing. A neuron depolarizes(fires) and a muscle fiber contracts. It’s all or nothing. A neuron doesnt partially fire nor does a muscle fiber partially contract. When you’re lifting a progressively heavier amount you’re not contracting that muscle more, you are recruiting more muscle fibers within the muscle you are targeting. This is fact. It’s a definitive physiological fact and it supports the OP in that for optimal adaptation and growth the goal is 100% recruitment of the muscle fibers of that particular muscle you are training. Common sense sais 100% recruitment will occur in the 5-0 (or 7-0) reps before failure range. Those studies serve to back up basic physiology.

It’s not that you won’t grow if you don’t train to this level, and I believe the OP made that clear. But if you want to maximize your hypertrophy, then yeah. You need to push for 100% recruitment of muscle fibers in your targeted muscle. And that, gentlemen, is going to occur during the few reps before failure.

I hope this article clears up a lot of the confusion and misconceptions regarding these various terms and the topic of hypertrophy and that folks find it useful.

Sources directly cited, referenced, or used in this article.

Maximizing Muscle Hypertrophy: A Systematic Review of Advanced Resistance Training Techniques and Methods. Int J Environ Res Public Health. 2019 Dec 4;16(24):4897. doi: 10.3390/ijerph16244897. PMID: 31817252; PMCID: PMC6950543.

Exploring the Dose-Response Relationship Between Estimated Resistance Training Proximity to Failure, Strength Gain, and Muscle Hypertrophy: A Series of Meta-Regressions


Chris Beardsley - How many stimulating reps are there in each set to failure?

Muscle Activation Strategies During Strength Training With Heavy Loading vs. Repetitions to Failure


The force, tension, nor the mass can increase if there is a reduction in acceleration.

It just cant.

That exxcerpt is a note from another member on the topic.
He did misspeak when saying force would increase in the listed function.
but the underlying premise when discussing the topic of hypertrophy is still sound.
as acceleration slows you are naturally increasing the mechanical tension through TUT causing the majority of adaptation.

I politely disagree.

Our work capacity or ability to move weight at rate changes, but none of the physical properties change.

Consider this- there is a simple mechanical device (linear drive) with a rope attached at one end, and a barbell at the other.

How many reps does it take to change the tension through the rope?

The answer is, it doesn’t change.

I think you need to imagine the linear drive with lots and lots of ropes. And at first you’re only pulling on some of the ropes. So there are some ropes under tension, and a bunch hanging all loose and floppy.

And tension “increases” as you start pulling on more and more of the loose, floppy ropes. As they go from unrecruited to recruited and taught.

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mechanically, from a physics and engineering standpoint, you are correct.

the tension, from a literal, mechanical sense, does not change.

what changes is the impact of that tension.
your example assumes that the rope is a constant and remains unchanged. Our muscles do not remain unchanged, as we approach failure more motor units must be recruited to complete subsequent reps and the effect of that tension is exasperated.
The numerical value of that tension is unchanged, correct, but the proportional impact of that tension is.

Like a series of blocks & tackles staged to increase applied force as the actuator moves through the range of motion. Sure.

I was really just commenting on the sketchy part.

Yes. This speaks to work capacity, not tension.

Not trying to be overly critical. Just pointing out some things that could use refinement if you want to publish.

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again, that particular portion of the article is simply a direct quote taken unedited from another members comment on the original post.

while i agree its not literally correct, i felt that the perspective and premise may be found useful to some readers.

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Amazing article, thanks for reposting.


I have already read your post on other forum, but I’ll re-read it to print it in my brain (or that remains of its)