How Muscle Growth Actually Works (According to Science)

You know how to build muscle. I know you do. You lift heavy things, put them down, drink a shake, and pray to the gods of hypertrophy.

But how does a dumbbell curl actually tell your body to build bigger biceps? How does muscle growth work? In this article, I’ll explain what current science says about what makes muscles grow, minus the PhD jargon.

Tension to Translation

A new review called “Tension to Translation” breaks down how your body turns the stress of lifting into actual muscle growth.¹

It’s about the molecular biology (not magic!) that connects the external things you do (lifting and eating) to the internal stuff your cells do (signaling and growing).

It’s both simple and complex at the same time, but I’ve read the heavy science stuff, so you don’t have to.

The Big One: Strength Training

One thing is clear: strength training is the main driver of muscle growth. You cannot eat your way to big muscles.

But do you need to lift a house to get big as a house? No, you don’t.

Your muscles need to feel mechanical tension. That tension is what tells your body that you need bigger muscles to handle what you’re doing in the gym.

But it doesn’t matter much if you train heavy or light.

Heavy training works just fine, but research shows that you can get similar growth with lighter loads (down to ~30% of your 1-rep max) as long as you train close to failure.

That’s when you recruit the big motor units, and that’s where many of the growth signals happen.

The Volume Knob

So, if training load isn’t the main factor, what is?

Training volume.

To maximize hypertrophy, “volume load” (sets x reps x weight) is the most important variable.

More volume leads to more growth. At least up to the point where you can’t recover and burn out.

The problem is that no one can tell you exactly where your optimal training volume point is. It depends on many factors, including genetics and training experience, plus all the things you do outside the gym (nutrition, sleep, stress, and so on).

Playing around with things like rest intervals or exercise order can be useful for performance and to get enough volume in, but they don’t independently affect muscle growth.

Focus on getting enough high-quality sets in: train hard, get out of the gym, eat, and recover.

The Support: Dietary Protein

Even though your training is the number one factor for growth, you still need to provide the building blocks (amino acids) so your body can respond to the signals and actually build the new muscle tissue.

However, according to current research (and this review), protein plays only a “minor supporting role”.

Now, that doesn’t mean protein is irrelevant or that how much you eat doesn’t matter if you want to build muscle. On the contrary.

But first you need the stimulus – the training. Without that, pounding down a ton of protein won’t do all that much for muscle hypertrophy.

How Much, and When?

To maximize muscle growth, you want to aim for 1.2 to 1.6 grams of protein per kilogram of body weight (approximately 0.5 to 0.7 grams per pound).

Eating more than that doesn’t hurt, but you’ll get diminishing returns, and it might not help you build any more muscle (although a few individual studies have found potential small benefits of even higher intakes).

Also, old-school advice said you can only absorb 20 to 25 grams of protein at a time.

That’s hogwash. A recent study even showed that eating 100 grams of protein in one sitting kept muscle protein synthesis (MPS) elevated for at least 12 hours.²

So, don’t stress if you eat a massive steak. Your body will use it to build muscle, just over a longer period.

However, while those 100 grams lasted longer than 25 grams, they didn’t quadruple the muscle-building response. That suggests that there might still be an amount of protein per meal that maximally boosts MPS.

The authors speculate that 30–40 grams of protein per meal and spreading your intake out over the day might still be optimal if your goal is to build muscle mass.

Besides, I bet most people prefer reasonably-sized meals for practical reasons.

They also mention that whole foods (like whole eggs) might stimulate more growth than just egg whites or, say, an amino acid supplement, even if you end up with the same amount of protein.

There’s something in the “food matrix” (not the movies) that might matter. Turns out nature might know best after all.

What Happens Inside Your Body?

That’s all well and good, but how does a dumbbell (external) tell your DNA (internal) to build muscle?

Back in the day when I started training, I was taught that muscles grow when you create micro-tears in the muscle fibers in the gym, and the body then repairs them slightly bigger and stronger.

However, that “microtears cause growth” model is largely downplayed in modern exercise science.

It isn’t fully wrong, and muscle damage might contribute to growth, but it is no longer considered the main mechanism. It may even be counterproductive in some cases.

The microtears theory is still a very common one, though. For example, as a test, I asked ChatGPT (latest version) “how does muscle grow?” – the way most people would pose the question – and got this answer right now:

Again, this is an outdated explanation. Partly correct in some ways, but flawed in others.

How Does Muscle Growth Work: The Modern Model

So how does muscle growth work?

Through a process called mechanotransduction.

Basically, your muscle cells have different sensors that feel the mechanical stretch and convert it into chemical signals:

• Costameres and integrins are tiny structural bits on the edge of your muscle cells. They have this neat thing where they actually physically sense the stretch and squeeze when you train.
• Titin is a giant (well, “giant” in context; it’s still microscopic) protein that lies like a spring inside your muscle fibers and might sense the load and tell your genes to grow.
• Stretch-activated channels are like little gates in the muscle cell membrane. They open up when they get stretched, letting calcium rush in to start the muscle-growth-signaling cascade.

Meet the Foreman

The foreman of the entire muscle-building construction site is called mTORC1.

This guy receives the signals from the above sensors, triggered by your workout (the mechanical stress) and your diet (the amino acids from the protein you eat), and gives the go-signal for your muscle cells to start building new muscle protein.

And the language your muscles speak to make this tiny construction crew understand what to do is, as we talked about earlier, mechanical tension.

If you’re not creating that tension by training hard and close to failure, those little sensors never get the memo to wake up the foreman. And then your muscles have no reason to grow bigger.

Note that the review spends pages covering different aspects of this system, and I’m using mTORC1 as a stand-in for the whole shebang. It’s more complex than a foreman pointing at stuff to make things happen, of course.

Checklist for Gains

Based on this review, I’ve designed a straightforward and very simple cheat sheet to build muscle.

Of course, actually doing it takes a lot of hard work, but there is nothing super complex about getting big.

1. Lift Weights. ✅ No surprise. Strength training is the primary driver of muscle growth. You can do other forms of exercise until you’re blue in the face (and you should; maybe not the blue-in-the-face part, but cardio is great for your health), but it won’t signal hypertrophy like lifting.
2. Train to or Close to Failure. ✅ The weight on the bar matters less than how much effort you put in. Light or heavy, you gotta train hard. And the lighter you go, the more important it becomes to really get close to failure to recruit all your muscle fibers.
3. Volume Matters. ✅Track your weekly sets. It’s the easiest way to stay on top of your training volume. If you stop growing and you know you’re doing everything else (like diet and recovery) right, you might need to up your training volume a bit.
4. Eat Your Protein. ✅ Aim for ~1.6 g/kg (0.7 g/pound) of body weight every day to give your body the building materials it needs to grow. But remember that protein isn’t everything: you need enough calories, essential fats, and micronutrients (vitamins and minerals) as well.
5. Don’t Overcomplicate the “Anabolic Window”. ✅ Timing your protein intake around your training is much, much less important (if at all) than getting enough protein over the day as a whole.

Nail those points, and get the rest and recovery your body (and brain) needs. If you do that, your body will translate them into gains at the speed your genetics allow.

And don’t forget to log your training to track your volume and progression, so you know what’s working and what’s not, and can make changes if and when you need to, before you reach a plateau.

The best way to do so is with StrengthLog, our workout log app.

Track Your Training. See Real Progress.

Log your workouts in one place and watch your numbers climb, week after week.

• Free to get started
• Fast workout logging
• Cardio and strength training
• Free weights and machines
• Progress over time, personal bests
• Beginner-friendly training programs and workouts for every fitness goal

Download StrengthLog free:

It’s also filled to the brim with training programs that work, so you can focus on lifting and growing, not fiddling with spreadsheets.

Thanks for reading, and see you in the gym!

Want more?

Subscribe to our weekly newsletter to get notified of new articles, and get weekly training tips!

Last reviewed: 2025-12-05

References

1. Physiology (Bethesda). 2025 Dec 1. Tension to Translation: External to Internal Processes in Muscle Hypertrophy.
2. Cell Rep Med. 2023 Dec 19;4(12):101324. The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans.