This article is an excerpt from the new third editions of Bigger Leaner Stronger and Thinner Leaner Stronger, my bestselling fitness books for men and women.

Never cease chiseling your own statue.

—PLOTINUS

If you’ve spent any amount of time in the fitness space, you’ve heard a lot of things about muscle building.

Things like:

  • Muscles respond differently to different types of training.
  • Muscles don’t know weight. They only know tension.
  • There are different types of muscle growth.
  • Training with lighter weights and higher reps is best for muscle gain.
  • Training with heavier weights and lower reps is best for muscle gain.
  • Muscle building is mostly genetic, and how you train doesn’t much matter.

And you’ve also probably heard that most of that is pseudoscientific nonsense, and that some other theory or model altogether is the real “secret” to gaining muscle quickly and effectively.

If this has left you confused and frustrated, unsure of what to believe (and do in the gym) and what to ignore, I understand. I’ve been there.

Fortunately, while the physiology of muscle growth is tremendously complex, the science of gaining muscle is far simpler. In fact, at least 80 percent of effective muscle building comes down to understanding and applying a handful of laws that are as certain, observable, and irrefutable as those of physics. 

When you throw a ball in the air, it comes down. When you apply the three principles you’re going to learn in this chapter, your muscles grow bigger and stronger.

It’s that simple.

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Law #1
There Are Three Ways to Stimulate Muscle Growth

The first thing you need to understand about the physiology of muscle building is there are three primary “triggers” or “pathways” for muscle growth:

  1. Mechanical tension
  2. Muscle damage
  3. Cellular fatigue

Mechanical tension refers to the amount of force produced in muscle fibers. 

When you lift weights, you produce two types of mechanical tension in your muscles: “passive” and “active” tension. Passive tension occurs when your muscles are stretching, and active tension occurs when they’re contracting.

Muscle damage refers to microscopic damage caused to the muscle fibers by high levels of tension. 

This damage requires repair, and if the body is provided with proper nutrition and rest, it’ll make the muscle fibers larger and stronger to better deal with future bouts of tension.

(It’s still not entirely clear whether muscle damage directly stimulates muscle growth or whether it’s just a side effect of mechanical tension, but as of now, it deserves a place on the list.)

Cellular fatigue refers to a host of chemical changes that occur inside and outside muscle fibers when they contract repeatedly. 

When you repeat the same movement over and over again to the point of near failure, this causes high amounts of cellular fatigue.

Research conducted by scientists at Harvard Medical School shows that mechanical tension is the most important of these three pathways for muscle growth. This has been confirmed in a number of other studies as well. 

In other words, mechanical tension produces a stronger muscle-building stimulus than muscle damage and cellular fatigue.

These three factors also relate to what scientists call the “strength-endurance continuum,” which works like this:

  • Heavy, lower-rep weightlifting primarily increases muscle strength and results in higher amounts of mechanical tension and muscle damage, but less cellular fatigue.
  • Lighter, higher-rep weightlifting primarily increases muscle endurance and results in lower amounts of mechanical tension and muscle damage, but more cellular fatigue.

Given what you just learned, which style of training do you think is more effective for gaining muscle over time? That’s right—heavy, lower-rep work, because it produces more mechanical tension than lighter, higher-rep work.

You can find plenty of evidence of this in the scientific literature. 

For example, in a study conducted at the University of Central Florida, scientists separated 33 physically active, resistance-trained men into two groups:

  1. Group one did four workouts per week consisting of four sets per exercise in the 10-to-12-rep range (70 percent of one-rep max).
  2. Group two did four workouts per week consisting of four sets per exercise in the 3-to-5-rep range (90 percent of one-rep max).

Both groups did the same exercises, which included the bench press, barbell squat, deadlift, and seated shoulder press, and both were instructed to maintain their normal eating habits.

After eight weeks of training, researchers found that the second group gained significantly more muscle and strength than the first group. 

The scientists suggested two main reasons for why the heavier training beat out the lighter in not only strength gain (not surprising) but muscle gain as well:

1. Higher amounts of mechanical tension in the muscles

The lighter training, on the other hand, caused higher amounts of cellular fatigue.

2. Greater activation of muscle fibers

This results in greater muscle growth across a larger percentage of the muscle tissue.

Similar findings have been demonstrated in other studies as well.

This brings us back to your primary goal as a weightlifter: to get stronger, and especially on key whole-body exercises like the squat, deadlift, and bench press. 

The more weight you can push, pull, and squat, the more muscle definition you’re going to have.

That isn’t to say that lighter weights and other training methods have no place in your workout routine, but if your goal is to gain muscle as quickly as possible, the best way to do this is to gain strength as quickly as possible.

Law #2
Muscles Don’t Grow in the Gym

You might have heard this old bodybuilding adage before. 

There’s truth in it. Weightlifting alone doesn’t make your muscles bigger and stronger. That’s what happens after the workouts, when your body repairs the stress and damage they cause.

Every day, your body is constantly breaking down and rebuilding muscle proteins. This process is known as protein turnover, and when viewed on the whole, protein breakdown and synthesis (creation) rates generally balance each other out.

This is why the average, non-exercising person doesn’t gain or lose muscle at an accelerated rate.

Mechanically speaking, muscle growth is the result of protein synthesis rates exceeding breakdown rates over extended periods of time.

In other words, if your body is creating new muscle proteins faster than it’s breaking them down, you’re gaining muscle (and if it’s breaking them down faster than it’s creating them, you’re losing muscle).

Therefore, if you want to gain muscle as effectively as possible, then you want to do everything you can to keep protein synthesis rates at or above breakdown rates. The more time your body spends in this anabolic state, the faster you gain muscle.

When you do resistance training or cardiovascular exercise, protein synthesis rates decline during the workouts. Then, both protein synthesis and breakdown rates rise soon after you finish, with breakdown rates eventually overtaking synthesis rates. 

In this way, exercise is a catabolic activity, especially with longer workouts, and repair, recovery, and growth can only occur after.

Unsurprisingly, sleep plays a vital role in this process, because much of what your body does to recuperate and rebuild happens in bed. This is why studies show that sleep deprivation directly inhibits muscle growth (and fat loss) and can even cause muscle loss. 

Interestingly, these negative effects become even more pronounced when you’re in a calorie deficit.

Furthermore, research shows that even a single night of poor sleep can interfere with your performance in the gym, and two nights is enough to ruin it. Multiple studies have also clearly demonstrated that athletes who get enough sleep perform the best.

Law #3
Muscles Don’t Grow Unless Properly Fed

Most people think that calories only count when you’re talking weight loss. 

What they don’t realize, though, is that if you don’t eat enough, your body can’t do many things as effectively, including everything it needs to do to recover from your workouts. 

This is why research shows that when you’re in a calorie deficit, your body’s ability to repair and grow muscle tissue is impaired. This is also why workouts take a bigger toll on you when you’re dieting, and why intermediate and advanced weightlifters have to accept slow or no muscle gain when dieting to lose fat.

Remember that calories are what fuel every process in your body, and the system for muscle building is metabolically expensive. Therefore, if you want to maximize muscle growth, then you need to make sure you aren’t in a calorie deficit.

The best way to do this is to deliberately eat a bit more calories than you’re burning every day. This ensures that your body has all the energy it needs to push hard in the gym and recover from your workouts.

Another vital aspect of “feeding your muscles” is eating enough protein. In fact, this is just as important as eating enough calories, if not more so.

Carbohydrate also contributes to your muscle-building efforts. One of the substances that carbs are converted to in the body is glycogen, which is stored in the muscles and liver and is the primary source of fuel during intense exercise.

When you restrict your carb intake, your body’s glycogen stores drop, and studies show that this inhibits genetic signaling related to postworkout muscle repair and growth.

When you’re exercising regularly, restricting your carbs also raises your cortisol and lowers your testosterone levels, which further hampers your body’s ability to recover from your workouts.

All this is why research shows that athletes who eat low-carb diets recover slower from their workouts and gain less muscle and strength than those who eat more carbs.

It’s also worth mentioning that eating a low-carb diet will reduce your strength and muscle endurance, which makes it harder to progressively overload your muscles in the gym and thereby maximally stimulate muscle growth.

And what about the final macronutrient, dietary fat?

Some people say a high-fat diet is conducive to muscle gain because of its effects on anabolic hormone production, testosterone production in particular.

When you dig into the research, however, you quickly realize that these effects are far too small to make a noticeable difference in the gym.

Furthermore, the more dietary fat you eat, the less carbs you’ll be able to eat, which will more than wipe out any potential muscle-building benefits from slight hormonal upticks.

#

You can spend hundreds of hours studying muscle growth and barely scratch the surface. It’s extremely complex and involves scores of physiological functions and adaptations.

Fortunately, you don’t need to be a scientist to have a working understanding of the research and to be able to use it to gain whole-body strength and muscle. 

You now have the foundation of this understanding. You overload, damage, and fatigue your muscles in your workouts, and then feed and repair them after. 

This also brings us to the end of part two of this book, and I want to congratulate you on making it this far. You’ve digested a lot of information and gained a whole new perspective on fat burning and muscle building.

If you’ve been enjoying yourself, then you’re going to absolutely love what I have in store for you next.

In the third part of this book, we’re going to take a break from the physiology of fitness and dive into the psychology, because if you don’t “get your mind right,” you’re probably never going to “get your body right.”

Key Takeaways

  • There are three primary “triggers” or “pathways” for muscle growth: mechanical tension, muscle damage, and cellular fatigue.
  • Mechanical tension refers to the force you apply to your muscles against a resistance.
  • Muscle damage refers to microscopic damage caused to the muscle fibers by high levels of tension.
  • Cellular fatigue refers to a host of chemical changes that occur inside and outside muscle fibers when they contract repeatedly.
  • Mechanical tension is the most important of these three pathways for muscle growth.
  • Heavy, lower-rep weightlifting primarily increases muscle strength and results in higher amounts of mechanical tension and muscle damage, but less cellular fatigue.
  • Heavy, lower-rep work results in more muscle gain because it produces more mechanical tension than lighter, higher-rep work.
  • Muscle growth is the result of protein synthesis rates exceeding breakdown rates over extended periods of time.
  • Exercise is a catabolic activity, especially longer workouts, and repair, recovery, and growth can only occur after.
  • Sleep deprivation directly inhibits muscle growth (and fat loss) and can even cause muscle loss.
  • If you want to maximize muscle growth, you need to make sure you aren’t in a calorie deficit.
  • A vital aspect of “feeding your muscles” is eating enough protein, and this is just as important as eating enough calories, if not more so.
  • One of the substances that carbs are converted to in the body is glycogen, which is stored in the muscles and liver and is the primary source of fuel during intense exercise.
  • When you’re exercising regularly, restricting your carbs raises your cortisol and lowers your testosterone levels, which hampers your body’s ability to recover from your workouts.
  • A low-carb diet will reduce your strength and muscle endurance, which makes it harder to progressively overload your muscles in the gym and thereby maximally stimulate muscle growth.
  • The more dietary fat you eat, the less carbs you’ll be able to eat, which will more than wipe out any potential muscle-building benefits from slight hormonal upticks.

This article is an excerpt from the new third editions of Bigger Leaner Stronger and Thinner Leaner Stronger, my bestselling fitness books for men and women, which are currently on sale for just 99 cents.

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