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You Need to Know This About the 3 Muscle Growth Mechanisms

Updated: Mar 9, 2022

If you're into strength training in the gym (or anywhere else), you'll often hear people talking about the 3 primary mechanisms of muscle growth.

Heck, we even talk about them often here at Gympulsive too.

But just what exactly are they are why are they so important?

What does this all mean for me?

Keep on reading below to find out in this post!

Fit and strong man doing barbell curls to build muscle in his biceps using the three mechanisms of muscle growth

The 3 Primary Mechanisms of Muscle Growth

Mechanical Tension

This is the primary and most important mechanism of muscle growth.

Basically, mechanical tension refers to the amount of weight that you're lifting with your muscles and the number of reps that you're able to achieve with that given weight (both indicators of muscular strength)

The time that your muscles spend under tension provided by the weight (dumbbells, barbells, your bodyweight, etc.) place mechanical tension on your muscles.

For example, if two people are bench pressing and one of them is lifting 20kg or 45lb more than the other, the stronger presser is placing more mechanical tension on their muscles.

However, you also need to ensure that you're going through a full range of motion and are loading your muscles in both their shortened and lengthened positions to build muscle most optimally.

To get stronger and build muscle over time, you absolutely have to be progressively overloading your workouts and adding to the mechanical tension that you're placing on your muscles.

For example, if you're able to double the weight that you can bench press for a rep range that's conducive to hypertrophy (6-15+), your chest, shoulders and triceps would've grown in size.

Strong and muscular man doing barbell bench press in a gym, placing lots of mechanical tension on his muscles

However if you aren't able to gain any strength at all and your numbers stay the complete same, you won't have grown very much, if any at all in terms of muscle building.

Muscle strength and muscle size are directly related to each other, and you can read all about that here in this blog post.

The Key Takeaway: The primary driver of muscle growth is metabolic stress. That is the amount of weight that you lift through a range of motion and the number of reps that you get. To build muscle, you have to be getting stronger over time and continually increasing your lifting capacity.

Metabolic Stress

Metabolic stress is the next primary driver of muscle growth.

This term refers to a sustained effort in your muscles to continue producing force, even when energy becomes low and you start to tire out.

Metabolic stress is responsible for that 'burning' sensation that you feel in your muscles when you lift moderate or relatively lighter weights for in a higher rep range.

And although this is usually associated with bodybuilding, you'll see people training for metabolic stress if they're endurance athletes, or people that often have to sustain physical efforts for extended periods of time.

As you begin to tire out but continue to produce force, your body naturally creates a buildup of metabolites such as lactate and ethanol.

This causes the burning sensation and results in metabolic stress placed on your muscles.

The more of a burn you feel in your muscles, the more metabolic stress you're placing on them and the more results you're likely to see.

The Key Takeaway: Metabolic stress is the second most important mechanism of muscle growth, and stems from continually producing force, even when your muscles start to tire out and lose oxygen. Metabolic stress is responsible for the burning sensation that you feel in your muscles during moderate to high rep ranges. The more of a burn you feel, the more results you're likely going to see from your hard work.

Muscle Damage

Although this is the third primary driver of muscle growth, it's still an integral part of muscle building that you definitely need to be aware of if you're serious about reaching your goals.

Fit bodybuilder doing single arm dumbbell row to build muscle and cause muscle damage in her back and biceps

Muscle damage happens when you place stress on them, and takes place during both the eccentric and concentric portions of your movements.

Eccentric: the part of a movement where your muscle is lengthening (the downward phase of a lift).

Concentric: the part of a movement where your muscles are shortening (the upward phase of a lift).

Examples include:

Bicep Curl

  • Curling upwards is the concentric portion of the lift

  • Lowering the bar back down is the eccentric

Barbell Bench Press

  • Pressing the weight up is the concentric portion of the lift

  • Lower the bar down to your chest is the eccentric

Lat Pulldown

  • Pulling the bar down towards your chest is the concentric (the bar moves down, but the WEIGHT itself moves up)

  • Allowing the weight to drag the bar back up is the eccentric portion of the lift

Now that you know what eccentric and concentric portions of an exercise are, we can move onto the next part of the explanation.

If you're an avid lifter (or even trained intensely just once), you'll have experienced DOMS before.

This term stands for Delayed Onset Muscle Soreness, and is a result of all the muscle damage that you cause when you work your muscles through resistance training (whether that's with external loads or your own bodyweight).

DOMS serves an an indication that you properly hit your muscles and were able to achieve muscle damage through your training.

But don't worry if you don't experience DOMS after a session.

That doesn't necessarily mean that your workout was ineffective at stimulating results.

NOT experiencing DOMS is not an indication that your workout was bad.

When we go through resistance training, our muscles suffer micro tears (don't worry, this isn't a bad thing) and damage that has to be repaired for growth.

And while muscle damage does occur in both portions of a lift (eccentric and concentric), the eccentric phase of a lift actually does cause more muscle damage in all exercises.

This is why people will perform exercises intentionally with weights that they usually wouldn't be able to handle and only go through the negative portion of a rep.

For example, jumping negative pull ups are a great way to build foundational strength and muscle mass for people that aren't yet strong enough to do a proper and full pull up.

And some bodybuilders will also do exercises such as heavy cheat curls to focus on the eccentric portion of the movement, and resist the weight as much as they can.

The muscle damage caused by your training activates protein synthesis and encourages your muscles to grow in size, which is achieved through adequate recovery and rest.

The damage will be repaired, and your muscles will actually be repaired to a size slightly larger than before so that they can tolerate more stress the next time before reaching failure.

The Key Takeaway: Muscle damage is also one of the primary causes of muscle growth. It's achieved through both eccentric and concentric phases of a movement, but is more common in the eccentric or lengthening phase of a movement. DOMS can serve as an indication that you hit your target muscles properly and were able to achieve some proper muscle damage for growth in the future, but aren't necessary for gains.

So What Does This Mean For Me?

We'll start by telling you that these 3 mechanisms definitely can and will overlap or happen at the same time.

For example, during a set of heavy bench presses you're placing lots of mechanical tension on the chest, shoulders and triceps, but still causing lots of muscle damage and potentially DOMS the following day.

You'd also be placing metabolic stress on your muscles, but likely not very much as you wouldn't be working for too long.

Or during a set of very light calf raises (maybe you're a runner or a cyclist), you'd be training for a lot of metabolic stress and causing lots of muscle damage, but not be placing very much mechanical tension on your muscles due to the light weight.

And all this information is going to be completely useless to you if you don't implement it into your training correctly.

To build muscle and reach your goals at the most optimal rate, you need to be training with the right mechanisms and using a combination of them all.

For example, if you're trying to build muscle, you should do a combination of both heavy and moderate/light lifting to work all three mechanisms of growth and get the most out of your workouts.

Again, you can learn all about this by clicking on the link to our blog post here.

Remember, to see long term progress you absolutely HAVE to be progressively overloading your workouts.

Very muscular and lean man applying progressive overload onto his deadlifts and training for muscle growth

Progressive overload is going to apply to all three mechanisms of muscle growth, and is vitally important for you to implement.

Put in the most basic terms, your body adapts to the stress that you place it under over time and grows to get stronger and fitter so that the next time you do the same exercise at that same intensity, it's not as difficult.

In order to keep on seeing progress and prevent plateaus, you have to be continually making your workouts more difficult to keep giving your body a reason to grow.

Otherwise it simply won't.

Final Thoughts

The three primary mechanisms of muscle growth are a concept that are pretty important for you to understand if you're serous about reaching your goals and really want to train at the most optimal level.

Understand the ideas in this article, implement the knowledge into your training and you'll be well on your way to becoming the most efficient lifting or trainee you can be!

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