The 3 Primary Muscle Growth Mechanisms

These are the 3 primary muscle growth mechanisms that lead to muscle growth.

So what is a “muscle growth mechanism”? Well, the mechanism is basically what causes muscles to grow.

And if we zoom out to look at the big picture, there are 2 things you need to build muscle:

Stimulus
Supplies

Next I’ll go into each of those parts in more detail.

Part 1: Stimulus for Muscle Growth

Your body isn’t going to grow muscle unless you give it a good reason to. We call that reason the “stimulus.”

And in this video, Brad Schoenfeld defines 3 mechanisms of muscle growth:

Muscle Growth Mechanisms, #1: Mechanical tension

This is probably the primary driver in muscle growth, and is related to the force that is placed on the muscle.

It has a few components:

The load (how much weight is on the bar)
Volume (how many reps & sets you do)
Time under tension (how fast/slow you do each rep multiplied by the total reps)

This is basically lifting more weight, for more reps, over time. (Progressive overload.)

Muscle Growth Mechanisms, #2: Metabolic stress

This is when you generate a metabolite buildup in your muscles which is a byproduct of training.

To achieve this, you need to do higher reps (until glycolysis kicks in), incomplete range of motion, or static holds.

It should cause a burning sensation.

Muscle Growth Mechanisms, #3: Muscle damage

This is where you create micro-tears within your muscles, and specifically happens during to the eccentric portion of the exercise (when you’re lowering the weight).

Many guys ignore the eccentric portion of the exercise, but it’s during this part of the lift—when your muscle is stretching under a load—that the most damage happens.

(This is also what makes you extremely sore.)

How Long Does The Exercise Effect Last?

In study #1 below, researchers measured the protein synthesis rate (PSR) over time and found that PSR was elevated over baseline for over 2 days:

112% at 1 hour
65% at 24 hours
34% at 48 hours

In order to take advantage of this increased PSR, you’ll need to make sure that your protein synthesis rate is greater than your muscle/protein breakdown rate.

And that leads us to part 2 of the muscle growth equation:

Part 2: Supplies for Muscle Growth

This simply means that if your body is to make muscle, it needs something to make that muscle out of. Raw materials, AKA amino acids (protein).

Researchers would say that “muscle hypertrophy occurs when the overall rates of protein synthesis exceed the rates of protein degradation.”

In other words protein synthesis > protein breakdown.

So if you want to build muscle, just eat 1000 grams of protein a day and you’ll be jacked in no time…right?

Sorry, wrong.

See, your body has pathways in place—complicated regulatory mechanisms—to prevent things from happening too suddenly, and to prevent bad things from happening. On one hand this prevents sudden healthy changes, like growing a lot of muscle really fast, but it also protects against unhealthy changes like cancer.

So there’s a limit to how much protein synthesis you can take advantage of.

Increasing protein from 50 grams to 150 grams/day will give you a big muscle-building advantage. But increasing from 150 to 250 will only give you a slight advantage (and maybe none at all).

In short you want to make sure you are maximizing that 48-hour post-workout “window of opportunity” by consuming protein with all the essential amino acids (and particularly leucine).

The Big Problem With Muscle Growth Studies

Many studies, like #1 in the references below, study the effect of different types of exercise on a group of study subjects. That particular study was comparing the effectiveness of concentric vs eccentric resistance exercise, and found that there was “no significant difference between contraction types.”

But there’s a problem with studies like these, which is that they are typically done using untrained volunteers. In other words, the people participating in this study are average guys & gals.

What works for your average Joe will NOT necessarily work for a highly trained weight lifter.

Case in point:

That study I just mentioned found no difference between concentric & eccentric movements. But we know that the eccentric (lowering the weight) portion of a lift causes more damage to your muscle.

Now that doesn’t matter for an average guy (as the study showed). But as you become more highly trained and get closer to reaching your genetic limit in terms of muscle growth, any small advantage you can get—such as focusing a little more on the eccentric portion of your lifts—is going to help you take the next step in your physique.

What Should You Do?

Very simply, you need to do 2 things:

Provide a stimulus (lift weights)
Provide supplies (healthy diet)

Of course this is a massive oversimplification. To progress beyond your easy “newbie gains,” you’ll need to follow a muscle growth program that is optimized to take advantage of all 3 of the muscle growth mechanisms described above…

…while also following a diet that provides sufficient supplies to take advantage of your elevated protein synthesis rate (without providing an overabundance that would lead to fat gain).

Make sense?

If you want a blueprint for how to do this in an optimal fashion, I recommend you check out The Stronger+Leaner Guide to Getting Ripped.