Muscle Hypertrophy Explained — The Art And Science Of Muscle Growth

By JC Deen



muscle hypertrophy
Image Credit: Satish Krishnamurthy (CC license)

If you want to know about the muscle building process works through various training ideas, all backed by science, then you’ll want to read this article.

In order to get muscles to grow, one thing is certain: You must stress your body.

A friend of mine once made a statement that was so simple, but it’s so true. Being as jacked as he was, someone asked him how he got that way. All he said was “Work out with weights. Stress your body. Eat enough to grow. Rest, recover, and repeat.”

And while that advice is not wrong, it’s not entirely clear and actionable.

In this article, I’m going to help you understand how muscle hypertrophy (muscle growth) happens, how to train properly, and what the science tells us about the muscle hypertrophy process.

Muscle Hypertrophy Is Both Art And Science

If you pay attention to the most successful bodybuilders, they all have something that is unique to them and their individual viewpoints about what works best for them. But they didn’t come to this conclusion their first week of training. It happened over many years of training and trying out different methods.

Some people gravitate toward certain movements for various reasons. Perhaps a movement helped them develop a lagging body part, or a particular rep scheme allowed them to make progress after a long plateau.

However they arrived at their ideas and personal idiosyncrasies is due to lots of testing, tinkering, and personal temperaments.

A quick example is while some people have built amazing bodies on mostly full-body training, others have utilized body part splits as their preferred method. The training modality differs a great deal, but the end result of more muscle and more strength are fairly similar in comparison.

Some people will scoff at me right now and exclaim “but the science says full body training is better than body part training.”

And that’s fine because some research says hitting a muscle group more frequently is ideal… But I’m here to help you understand that we don’t need a textbook full of studies to tell us how to get bigger and stronger. Most of the methods that have worked for a long time are now being validated via scientific studies.

But even if we had the science to back up the methods at the time, I don’t think the 70’s era bodybuilders would’ve had their noses in the training books. They’d likely be spending that time in the gym or in the park training their asses off.

I don’t need a pubmed study to tell me (neither do you) that pushing oneself on the squat, bench and deadlift is going to make my legs, glutes, chest, traps, and lats bigger.

Many times when someone has a preferred training style, it comes down to the idea of “what works best for them” and what that usually translates to is one or more of the following factors:

  • Work schedule
  • How often they can train or go to the gym
  • Their recovery ability
  • Training preferences
  • Lifestyle factors (job, family, commute)
  • Stress levels

Regardless of what factors above dictate how and when you train, here’s what every person who’s successfully built muscle over their lifetimes ALL have in common:

  • They trained with intensity (adding weight to the bar, increasing total volume, and approaching failure with their training).
  • They were very consistent and made training a lifestyle (years of consistent training, not a few months here and there).
  • They varied their training over time to help induce new muscle growth stimulus and avoid adaptation and injuries.
  • They were methodical in their approach, meaning they paid attention to rep schemes, tracked their progress, and aimed to improve over and over again.

Since training programs and approaches will vary amongst individuals, let’s bypass the art of hypertrophy for now and take a look at the science.

“Build Strength And The Size Will Come”

muscle hypertrophy

On this here Internet, there’s a lot of opinions about what matters more when it comes to training for size, and many will say that if you only get strong, you’ll also get big, but that’s not always the case.

One study, The problem Of muscle hypertrophy: Revisited., tells us the following:

  1. There’s a weak correlation between the change in muscle size and the change in muscle strength after training.
  2. There seems to be ample maintenance of muscle strength despite loss of muscle mass with detraining.
  3. There are similar levels of muscle growth between low-load and high-load resistance training, yet divergent results in strength.

When looking at point #1 above in the real world, there are competitive powerlifters in the light weight classes that are much stronger than bodybuilders with similar bone structure and frames. And when you compare them side by side, the bodybuilders are much more muscular but oftentimes less strong.

As for point #2, strength is very much a skill because it requires the activation of your nervous system. And the nervous system can be trained, just like a muscle can be trained. Athletic movements such as running and jumping are skills that have to be developed. Sprinting and other athletic skills take practice.

Lifting a barbell in a certain motion such as the squat, bench, or deadlift can be trained in a similar manner that you would learn any other skill. It takes a lot of focused practice, exposure to the movement many times over various periods, and usually requires specific techniques that allow you to lift more weight over time.

As a result, you’ll find Olympic lifters training daily, oftentimes practicing their movements 4-6 times over a 7 day period. Yes, that means squatting, pulling and other accessory movements daily.

And point #3 leads into another study I found pretty interesting.

Volume Dictates Muscle Gain, Not Load Alone

In this study, Effects of different volume-equated resistance training loading strategies on muscular adaptations in well-trained men., we see quickly that pure strength-focused training and bodybuilding training both elicit similar gains in musculature when the volume is similar. Pay attention to the bold.

Quick Note: Volume is the total amount of sets and reps over a defined period of time. In this case, 3 sets of 10 equates to 30 total reps, just as 10 sets of 3 also equates to 30 total reps.

In this study, they took 17 men and randomly assigned them to a so-called hypertrophy program following 3 sets of 10 with a 90-second rest interval between sets, and the others were on a strength-focused program of 7 sets of 3 (very heavy loads) with 3-minute rest intervals between sets.

And this is what they ended up with:

“In conclusion, this study showed that both bodybuilding- and powerlifting-type training promote similar increases in muscular size, but powerlifting-type training is superior for enhancing maximal strength.”

When you look at the total volume, one group did 30 total reps, while the strength-focused group did 21 total reps. But those who focused on the heavier loads (7 sets of 3) ended up building more strength.

But again, since volume was similar, they ended up seeing similar rates of muscle growth. And this leads me to another study…

Going To Failure Seems To Matter Most For Muscle Growth

In this study, Neither load nor systemic hormones determine resistance training-mediated hypertrophy or strength gains in resistance-trained young men., it suggests that the total loads (how heavy the weights are for you) do not dictate muscle hypertrophy as much as taking training to failure does.

So whether you’re using very heavy loads (your 3-rep max), or light loads (your 15-rep max), what seems to dictate overall muscle growth is how close you come to momentarily muscular failure, meaning you reach a point in the set where you can no longer finish another rep with good form.

From the paper:

“Our data show that in resistance-trained individuals, load, when exercises are performed to volitional failure, does not dictate hypertrophy or, for the most part, strength gains.”

Lastly, let’s talk about exercise variation…

You Gotta Keep Your Muscles Guessing, Bro

muscle hypertrophy

In this study, Changes in exercises are more effective than in loading schemes to improve muscle strength., we have an interesting finding that basically states that intensity matters most when it comes to training for hypertrophy.

The study left us with the following:

“Our findings suggest: (a) CIVE is more efficient to produce strength gains for physically active individuals; (b) as long as the training intensity reaches an alleged threshold, muscle hypertrophy is similar regardless of the training intensity and exercise variation.”

CIVE = Constant Intensity, Varied Exercise.

An example of this is as follows.

Let’s say you’re doing incline dumbbell presses using a weight you can comfortably do for sets of 8-10 reps, and each set you’re pushing yourself toward the top of the rep range, going to momentary muscular failure. That’s the intensity you want.

Momentary Muscular Failure, simply put, is the point in which you cannot perform another repetition with good and proper form.

In order to reap the rewards of changing your movement and getting the same benefit, you’d switch to a Smith incline press, a barbell incline press, or even a machine press, while still focusing on generating enough intensity by going to near failure on each set.

Intensity can come from lifting heavy loads over many sets, or lifting lighter loads over a few sets. It can also come from shortening rest periods, but for sake of explanation, here’s what I mean by intensity:

‘Intensity,’ here, is the X factor, the single variable that could have the greatest impact on your training results.

When it comes to resistance training, there are multiple ways to raise the intensity. The measures of intensity are:

  • Total weight lifted: whether a barbell, dumbbell, machine, or bodyweight (easiest to understand)
  • Rate of perceived exertion (not always the easiest based on varied perception)

When you think of intensity in terms of weight being lifted, you can easily increase intensity by increasing the weight — simple, right? This is because a dumbbell that weighs 10 pounds will require more effort, and thus, intensity from you to lift than one that weighs 3 pounds.

The second measurement, perceived exertion, is where it becomes tricky.

Another way of understanding this is how you feel during exercising by using the RPE (rate of perceived exertion) scale.

The scale spans 1-10, 1 being least amount of intensity, and 10 being the most intensity possible.

The scale:

0 – Nothing at all

0.5 – Just noticeable

1 – Very light

2 – Light

3 – Moderate

4 –   Somewhat heavy

5 – Heavy


7 – Very heavy



10 – Very, very heavy

In general, to make your training the most effective, you ideally want to work toward the RPE of 7-9 during your training. The above scale counts mostly for the heaviness of the loads, but you can also measure it in how fatigued you are. So if you’re doing a superset, alternating 2 movements back to back with very little rest between sets, you’ll notice yourself fatigued.

There are multiple ways to increase your intensity:

  • Adding weight to the bar (easiest to understand)
  • Using drop sets (starting with a heavy weight, and descending to lighter weights)
  • Shortening rest periods
  • Chasing the ‘pump’ (forcing blood into the muscles through high-rep training)
  • Using supersets (2 exercises done back to back with little rest)
  • Using tri-sets (3 exercises done back to back with little rest)
  • Giant sets (4 or more movements performed back to back with very little rest)
  • Circuit training (another name for giant sets)
  • Training with heavy loads (over 90% of your one-rep max)

As you can see, ramping up intensity can come in many different forms.

Without a doubt, gauging how you feel and how hard you push yourself during your training sessions is important.

At the same time, it’s important not to get hung up on whether or not the prescribed sets and reps was “enough,” because that sort of mentality tempts you to do more than is necessary. For some, this line of thinking is a free pass to push past their limits and put themselves at a high risk of injury.

As long as you’re pushing toward momentary muscular failure with each set, but not pushing past your limits, or having to get a spotter to lift the weight off of you ever set, you’re going to build muscle.

Questions And Answers

The following are some questions I got via email about training for muscle gain. If you have questions, feel free to subscribe here and email me anytime.

Q. “Are there any real differences in rate of muscle growth when comparing free weight exercises versus machine based exercises?”

A. It really depends but probably not. The thing is this… muscle growth happens through a process of Mechanical Tension, Metabolic Stress, and Muscle Damage. The definitions are as follows:

  • Mechanical Tension: Heavy strength training (heavy is relative to what is challenging for you). This is similar to the training of Olympic lifters and powerlifters — they train specifically for moving heavy loads. Any resistance against the muscle over a period of time is going to create tension.
  • Metabolic Stress: Typically achieved through mid- and high-rep training which induce fatigue and shortness of breath. It also causes the burning sensation, as you deplete oxygen in the muscles. You know how your muscles swell up after high-rep sets? That’s what we’re going for here. This feeling is also known as the pump to most gym rats.
  • Muscle Damage: Muscle soreness days after your training is usually indicative of the muscle damage, also known as delayed onset muscle soreness (DOMS). This is the results of micro-tears in the muscle tissue (a good thing, mind you). This mostly comes from the eccentric portion of a movement (lowering of the weight on a leg extension or bicep curl), so try to keep your eccentrics slow and controlled during your high-rep sets.

The reason I say probably not above is because people are getting jacked using all kinds of different movements. Resistance, volume, and accumulated time training is what matters most.

This is why there are construction workers who have big arms and backs from lifting heavy machinery and supplies for years on end.

It’s why you have gymnasts, who are absolutely jacked, that train a majority of the time using bodyweight exercises, and with rings.

muscle hypertrophy

Another thing to remember is your body doesn’t know the difference between a squat and a leg press, or a machine bench and a barbell. It only reacts and adapts to the tension and load that provides the stimulus for growth.

Q. “What would be the optimal amount of sets/reps/volume to use when training a muscle twice a week, and priority is hypertrophy?”

A. For the most part, anywhere from 30-60(ish) reps per body part, per session is a good starting point. In LGN365, my muscle gain programs are built around this number range over 2 upper/lower splits, 1 full-body split, and a 3-on, 1-off push/pull split.

Q. “Should a middle-aged man (one who is on HRT *hormone replacement therapy* and is probably past or at the end of his noob gains) expect to gain muscle?”

A. Yes, as long as you’re on a standard dose of testosterone that keeps your levels in a range that is good for you and determined by your doctor, and that you follow the principles of training I’ve outlined above.

Q. “How much does diet factor into hypertrophy?”

A. It’s just as important as the training because without enough food to help you recover and rebuild, the training alone is not going to cut it.

Here are some resources:

Q. “I feel like I already know the answer to this, but can an experienced lifter ever hope to gain some muscle while trying to lean out? Or is it the fruitless pursuit I expect it is?”

A. For the seasoned trainee who’s closer to their genetic potential than when they started, adding muscle while losing body fat is going to be very hard to accomplish. It can happen, but it’s best to focus on one goal at a time.

Q. “Can you tell me scientifically why muscles grow?”

A. I’m afraid no one can tell you exactly ‘why’ they grow. In fact, it’s still not completely clear, but we have lots of clues from all the people who’ve been training with weights, plus the scientific research that’s starting to confirm some of these ideas.

Also, see Amir Siddiqui’s eloquent way of expressing this here:

muscle hypertrophy

I believe someone posted this video in one of his groups and that was his response.

Q. Can I still build muscle with low testosterone levels?

A. You can, because women do it every day and they have much lower testosterone levels than men, but you won’t grow as quickly, nor as optimally if you would with healthy levels of testosterone. If you fear that your levels are low, first go get a blood test, then start to think about what changes you can make to increase them naturally.

Resources for further reading:

In the next few articles, I’ll be covering rep ranges, and how to plan your training blocks for muscle gain.

Until then, I’ll leave you with these:

The 5 Maxims Of Muscle Hypertrophy:

  1. Building Muscle Is Both An Art And A Science.
  2. Muscles Grow As A Response To Stressors (both self-imposed and from the environment).
  3. You Are Special, But You Are Not Unique.
  4. You’ll Grow As Long As You’re Willing To Change Your Mind.
  5. Time And Consistency Rule Above Everything Else For The Natural Trainee.

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JC Deen is a nationally published fitness coach and writer from Nashville, TN. Currently living in the blistering Northeast. Follow me on X/Twitter