3 Principles of Muscle Growth

3 Principles of Muscle Growth

My brother, Eric, was born almost exactly one year to the day after me.

Growing up, we played the same sports, watched the same movies, read the same books, went to the same schools, and even lived together during college.

We’ve always been close in age and interest, but we haven’t always agreed on everything. And while we’re cut from the same cloth, we’re wildly different physically.

Put our headshots together and you’d think we were twins. But we’re not so much alike outside our handsome faces.

At 6’ and 155 lbs, Eric has the body of an endurance athlete. I’m a bit...thicker, weighing 185 lbs at 5’10” — and that’s not by accident.

Eric and I train and eat differently because we have different goals. He likes being lean and ripped; I like eating big and moving tons of weight around in the gym.

If your goal is Eric’s sinewy physique, this post isn’t for you. But if you want to pack on pounds of muscle, keep reading. I’m about to tell you how to do it with science on your side.

And we’re going to get technical, so grab your reading glasses.

How to Build Muscle

Muscle fibers are comprised of myocytes — individual muscle cells — that contract and produce force when stimulated by your nervous system. When you lift weights in the gym, you damage those cells. In response, your body makes those cells bigger and stronger.

That’s why we lift weights: To stress muscles and force an adaptation, which results in bigger, stronger muscles.

Think about the last time you started a new workout program. I bet you got a lot stronger in the first 2-4 weeks, right?

This is a neuromuscular increase in strength. That means your body is getting better at recruiting the right muscle fibers at the right time with greater force. The changes in strength are REAL, but there isn't a lot of change in muscle size yet.

After those first few weeks of training on a program for gaining muscle have passed, the further increase in strength comes largely from an increase in muscle mass. This is the change in the body that we’re after! It’s called hypertrophy.

The Three Mechanisms that Stimulate Muscle Growth

There are three mechanisms that weight lifting triggers to increase muscle mass:

  1. Muscle damage
  2. Metabolic stress
  3. Muscle tension

Let’s look deeper into all three:

Muscle damage

Damage occurs to muscle fibers when you lift increasingly heavier weights. Specifically, the lowering of weight under tension, or the eccentric phase of a rep, causes micro-tears in the muscle fibers.

These micro-tears cause an inflammatory response, which signals your body to repair the damage, creating larger and stronger muscle fibers for future use.

This inflammatory response is critical for muscle growth, as it’s the first phase of the healing and rebuilding process. If you’ve been sore from strength training a couple of days after your last workout, you’ve been feeling that response!

Beyond exaggerating the eccentric phase of a lift, there are a few other ways to induce muscle damage, like lifting heavier weights than in your last session or targeting the same muscles from different angles (incline bench vs. flat bench).

But there’s one factor more important than any of the others:

Increasing the total amount of work done in each workout.

This amount is referred to as “volume” and is calculated as weight lifted x number of repetitions.

You can increase the volume of a workout by increasing weight, reps, or both. The key is that volume increases over time, and in an appropriate amount.

Adding too much volume too fast can backfire and cause excessive DOMS (delayed-onset muscle soreness).

Too much DOMS will make you want to (or have to) “take it easy” on your next workout. That means you’ll train with less intensity, volume, or both, leading to slowed progress toward your goal over the long-term.

Metabolic stress

The burning sensation we get after a set of an exercise is the “feeling” of metabolic stress. This is the “pump” that you’re after if muscle gain is your game.

During weight training, your muscles contract using energy sources provided by a process called anaerobic metabolism.

Anaerobic metabolism leaves behind metabolic waste, causing metabolic stress and creating an acidic environment around the muscle and swelling of the cells.  This, in turn, promotes muscle growth by prompting a hormonal response from the body to repair, rebuild and get bigger.

So how can you increase metabolic stress?

Easy. Get uncomfortable.

Push the last set of an exercise to the 12-20 rep range. You want to feel the burn here. It shouldn’t be easy!

You could also alternate same-muscle exercises (known as a superset).

For example — alternate between bench press and push-ups. After a set of bench press, immediately drop to the floor and perform a set of push-ups.

These methods aren’t comfortable, but they’re great for getting bigger!

Muscle tension

Imagine curling a 5lb dumbbell.

Now, imagine pulling a 300lb deadlift.

Can you feel the difference?

That’s muscle tension. The heavier an object is, the more muscle tension is required to move it.

Technically, muscle tension is the force felt in your muscles when pushing or pulling against a heavy object. Your muscles contract to produce force and pull on bones to create movement.

Muscle tension is highest when weight training in the 1-5 rep range with heavy weights and high loads.

This tension stimulates the growth of muscle by disturbing the cells mechanically and chemically, signaling further increases in size and strength.

What is the best program for muscle mass?

There isn’t a single best program, but there are some characteristics you want to see in any muscle-building program.

A solid hypertrophy training program effectively uses all three mechanisms mentioned above — along with appropriate rest — to introduce the greatest amount of stress to muscle cells and trigger the body’s response to build bigger, stronger muscle fibers for the next training session.

Here’s how you can add each of those mechanisms into your own hypertrophy program.

Muscle damage

  • Increase training volume (weight lifted x number of repetitions)
  • Emphasize the eccentric phase of reps.
  • Target the same muscle group from different angles.

Metabolic stress

  • Alternate same-muscle exercises (supersets).
  • Increase reps to the 12-20 range.

Muscle tension

  • Drop reps to the 1-5 rep range (with increased weight).

That’s how you use science to create the most effective muscle-building program possible. Have you been using these mechanisms in any of your programs? Let us know in the comments below!


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Andy holds a M.S. in exercise physiology as well as the coveted CSCS certification. He is a self-employed personal trainer and strength coach based in Nashville. When he's not coaching or working out himself, he's got his nose in a book or walking his dog, Jane, at the local park. He likes lifting heavy things, eating BBQ, and drinking local beer.

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