How Do Muscles Grow: The Science of Muscle Growth Explained


For most people, the main goals for lifting weights in the gym are usually to lose weight and gain muscle.

In this particular article, we’ll be exploring exactly how muscles grow and why most women are unable to gain large muscle mass even though they lift weights religiously.

First of all, it’s important to acknowledge the fact that there are various types of muscles in the human body, like the heart’s cardiac muscle, for example. However, for the purposes of this article, we’ll be discussing skeletal muscles only. The skeletal muscle is made up of a combination of sarcomeres which are responsible for fiber formation and contraction, as well as myofibrils, which is shaped like a thread.

The human body has 650 skeletal muscles which contract every time a signal is received from the sarcoplasmic reticulum part of the motor neurons. Basically, the motor neurons are responsible for communicating with your muscles so that they’re able to contract, and the clearer the communication is between these two parts, the stronger you become.

That’s why you’ll find that some powerlifters can actually lift ridiculous amounts of weights that are sometimes even twice their size. It’s because their muscles have gotten used to receiving signals to contract from the motor neurons. As a result, most powerlifters look small in appearance but are able to lift way more weight than bodybuilders.

It makes sense then, that practice does make it easier to perform certain movements over time, even though you gain most of your initial strength gains when you lift weights for the first time. And after those initial strength gains, it gets easier to grow your muscles by activating them on demand every time you train.

The Physiology of Muscle Growth

After each workout, your body starts to repair the muscle fiber that got damaged during the training session using a cellular process that involves fusing together muscle fibers in order to form new myofibrils or muscle protein strands. Once repaired, the muscle protein strands get thicker and larger to create those coveted muscle gains.

So essentially, muscle gains happen when muscle protein fusion is more prevalent than muscle protein breakdown. It’s interesting to note though, that this process of muscle hypertrophy (growth) only occurs during the rest period after your workout and not during.

So how are muscles added to the muscle cells? Well, what happens is that activated Satellite cells introduce more nuclei to the muscle cells thus adding to the growth of the muscle cells. The ability to activate these cells is essentially what separates those who gain muscle easily and those who have a hard time at it.

A recent study found that people that respond well to muscle growth get 58% myofiber hypertrophy from each exercise session, and their satellite cells were activated by up to 23%.  The same study found that those who respond modestly to muscle growth only saw 28% muscle growth in their satellite cells and only 19% activation. However, that’s not that bad when you consider that non-responders or those who don’t respond at all to muscle growth experience 0% muscle growth and 0% satellite cell activation after a workout. What this study shows is that your body’s ability to activate satellite cells is directly related to your ability to grow muscle. Of course, now you probably want to know what you can do to activate satellite cells in order to increase your muscle gains. Read on to find out.

3 Things That Make Muscles Grow

Repeatedly putting stress on the muscles has to be the foundation of natural muscle growth, because it works to upset homeostasis in your body. When your muscles undergo stress and homeostasis disruption, the following mechanisms happen to activate muscle growth:

Muscle Tension

The best way to grow your muscles is to introduce a stress load that is much greater than what your muscles are used to. How is this done? Well, what most people do is to lift heavier and heavier weights. Adding extra stress on the muscles literally transforms muscle chemistry in order to create an environment that is conducive to muscle growth and this includes the activation of satellite cells and mTOR.

Putting stress on the muscles will significantly affect the link between the muscle cells and the motor units. Here are two more effects that help to elucidate why some people can be stronger than others even though they might be smaller in stature.

Muscle Damage

That feeling of soreness after a workout signals localized muscle damage that you sustained during the workout. Immune stem cells and inflammatory molecules are released as a response to the muscle damage in order to trigger satellite cell activation. However, because this usually happens when your muscle cells have been damaged due to a workout doesn’t mean that you’ll have to feel sore after. The feeling of soreness tends to subside over time anyway due to other mechanisms.

Metabolic Stress

Feeling pumped or feeling the “burn” while you’re working out are usually signs that you’re experiencing metabolic stress, and this process is what causes the cells around the muscles to swell, thus leading to muscle growth that happens as the muscle cells grow. All the body does is to add some muscle glycogen to increase muscle size while encouraging the growth of the connective tissue as well. This specific growth process is called sarcoplasmic hypertrophy and is what happens when muscle growth happens in isolation from increased strength.

So, now that we understand that there are three primary mechanisms behind muscle growth, it’s time to find out what role our hormones play in muscle growth.

How Do Hormones Affect Muscle Growth?

Due to the fact that your hormones are somewhat responsible for regulating the activity of satellite cells, it only makes sense that they would play a pivotal role in muscle growth and regeneration too. Testosterone and Mecho-Growth Factor in Insulin Growth Factor are just two of the important muscle growth mechanisms to consider.

Most people who lift weights are aware of the influence of testosterone on their weightlifting process, and there is some evidence to suggest that testosterone intensifies the synthesis of protein, prevents protein breakdown, and fuels other anabolic hormones while triggering satellite cells.

Though 98% of the testosterone in your body is not available for use and is mostly found in the body, strength training is great at releasing testosterone while sensitizing muscle cell receptors to the suddenly available testosterone. Testosterone also helps to deliver more neurotransmitters to the area with damaged fiber so that they can activate tissue growth.

The Insulin Growth Factor, on the other hand, is great at activating satellite cells which encourage muscle growth and it also works to facilitate glucose uptake, stimulate the reception of amino acids (which is what creates protein) into the skeletal muscles and it improves protein fusion.

Two Forms of Growth

There are two mechanisms that are responsible for muscle growth and that is hyperplasia and hypertrophy.

Hypertrophy refers to muscle growth that occurs as a result of muscle fiber growth, whereas hyperplasia refers to a rise in muscle fiber numbers.

There are mainly two forms of hypertrophy and that is sarcomere hypertrophy which is characterized by a growth of the contractile part of the muscle, as well as sarcoplasmic hypertrophy, which is characterized by a growth of the non-contractile part of the muscle.

With sarcomere hypertrophy, you’ve got a small increase in the muscle’s diameter measurement accompanied by a significant increase in muscle density. Sarcoplasmic hypertrophy, on the other hand, indicates a significant surge in muscle diameter which is accompanied by a marked decline in density. Hypertrophy generally includes both of these processes, with the only difference being the ratio, which is contingent on how often and how hard you train.

Frequent, hard-core training will inevitably lead to solid gains, whereas only lifting weights in order to feel the “pump” will lead to soft muscles. The sarcomere is where it’s at if you want to improve your performance because sarcoplasmic hypertrophy is mostly useful when you just want to increase body weight without improving your performance.

Hyperplasia and What You Should Know

The process of hyperplasia happens when muscle fiber split to create more fibers that are the same size as the ones that they split from. Most say that the amount of muscle cells you have at birth is all you’ll ever have and that splitting cells only damages the existing fibers instead of creating new ones. Some sports scientists from Russia reported observing hyperplasia in the shoulders of swimmers who do high speed and low-resistance training, while other researchers were able to find hyperplasia in chickens that were hung by their wings for a few days. But hyperplasia is generally hard to predict in any case, and our best suggestion on the matter would be to try and train at high speed instead of trying to hang yourself on monkey bars for a weekend and see what happens.

Breaking Down

While there are a few theories on the subject, there is no general consensus on what the process of muscle growth consists of. However, most of the available evidence seems to suggest that the body’s muscles break down as a result of lifting and that the body spurs growth in order to protect itself from the future strain. Every 15 to 30 days, the human body literally breaks down and reconstructs its muscles. Lifting then creates an increased demand for fuel in order to accelerate this process. The reconstruction phase is at its peak in the 24 to 36 hours that follow your workout and can continue like that for up to 72 hours.

The well-known muscle hypoxia theory postulates that weight training leads to a drop in the oxygen levels of your muscles which is what activates protein synthesis. The theory is backed by the fact that blood flow gets temporarily shut off when you lift loads of over 60%. However, restricting blood flow using a tourniquet doesn’t necessarily lead to muscle growth and the muscle hypoxia theory becomes redundant in the face of that evidence. On the other end of the spectrum, other theorists believe that training creates an upsurge in blood flow and nutrient supply to the muscles, which then leas to muscle growth.

However, this one doesn’t hold up either because although running increases blood flow, you’re unlikely to come across a long distance runner with large legs.

Energetic Theory

The widely accepted energetic theory suggests that at any given time, there is a limited amount of energy available to your muscles for growth, repair, and movement. This has been referred to as current adaptive reserve. However, regular physical exertion can improve the body’s ability to reconstruct and break down muscles, which helps to increase current adaptive reserve, and when you have more energy you can get more done and can grow more muscles as well.

Training Volume

According to legendary Soviet weightlifting coach Medveyev, training volume is directly responsible for muscle growth. He even went on to suggest that a weightlifter who wants to remain in the weight class they’re in should train with singles, whereas a lifter who wants to progress onto the next weight class should do sets of 3 or 6 repetitions when training.

Another weightlifting expert Anthony Ditullio suggests that getting a high workout volume in a short amount of time, minimal rest between sets and following a strict exercise regimen, are all foundational aspects of muscle growth. However, one does need to have more energy in order to perform more work.

The most you can do in one second is a maximum single and it only leads to an insignificant protein breakdown. You also won’t need much fuel if you’re doing high repetition sets while carrying relatively light weights. On the other hand, you’ll need a larger fuel supply when you perform medium repetition sets with maximum weights, and that will lead to greater protein breakdown, an improved recovery of energy stores, and an upsurge in muscle growth.

During Your Training Session

As mentioned above, weightlifting is very stressful on the body, which is why it has to release hormones like testosterone, insulin-like growth factor, insulin, growth hormone, and cortisol after or during the weight training exercise.

The cortisol is responsible for breaking down carbs to create fuel, while the growth hormone works together with the insulin-like growth factor and insulin, to deliver more nutrients to the muscles in order to prevent breakdown. After the workout, a lot of growth hormone is released to regulate the release of insulin-like growth hormone, which acts as the main anabolic hormone. Testosterone triggers the nervous system to deliver stronger signals to rebuild muscle.

Insulin, insulin-like hormone and growth factor can all be utilized as performance enhancers to help grow muscle mass, and although the use of these hormones is prohibited, detecting them is hard.

The Long-Term Use of Supplements Could Have Serious Side Effects

As you’ve probably heard before, it’s important to have proper nutrition and get your protein in when training. The recommendation from nutritionists is that one should consume less than 1 gram of protein per kilogram of body weight to achieve good health. Consuming protein has a lot of benefits, from repair to growth and even hormone production, and the body can only use 20 to 30 grams of protein at any one time, except for when you’re fasting or are exercising, in which case your body stores up the additional protein as fat. That’s why it’s considered highly beneficial to eat several small meals during the day.

Liquid protein is often recommended because it’s easier for the body to digest liquids in greater quantities, and you can consume liquid protein during or after exercise. A bodybuilder named Michael Salvanti put on 20 pounds of weight in just four months due to consuming 8 ounces of his protein shake in liquid form, and this after he struggled to gain weight at all in the previous 4 years.

What Salvanti did was to incorporate his shakes into his training program, and research has shown that consuming carbohydrates and protein straight after a training session can significantly speed up recovery and increase insulin release.

Why Muscles Need Rest to Grow

Not giving your muscles enough time or rest to proper nutrition can actually defeat the purpose of what you’re trying to achieve and lead to your body going into catabolic state, which is destructive. Muscle protein responds to the impact of resistance exercise for 24 to 48 hours following the workout, so any meals that you eat during this period will play a huge role on how your diet affects muscle hypertrophy. Remember that the amount of muscle growth that you experience will also be limited by other factors like age, gender, and genetics. For example, men naturally have more testosterone than women, which makes it easier for them to build stronger and bigger muscles.

Why Fast Muscle Growth is Not Possible

For most people, muscles growth can take a long time, from several weeks to a few months just to experience the initial change, and this is due to your nervous system’s ability to trigger the muscles.

Also, genetics can play a role in this process through the satellite cell activation, hormonal output and muscle fiber volume and type. That’s why it’s important to get your lion share of protein by consuming essential amino acids and carbohydrates, as they’re responsible for regulating the reconstruction of the body’s muscle tissue from a cellular level.  Seeing noticeable muscle growth and a marked physical transformation happening to your body’s muscle structure is quite encouraging for many, but it’s also important to understand the science underpinning muscle growth.

A Conclusion on How Muscles Grow

In order to facilitate muscle break down and growth, you have to generate a new level of stress that it isn’t used to experiencing, thus forcing it to adapt. You can do this by lifting heavier weights, pushing your muscles to the limit and constantly switching up your exercise routine so that you can break down more muscle fibers than before. Once you’re done with the workout, make sure to give your body proper nutrition and ample rest so that your muscles can get a chance to rebuild and grow.

Secrets for Bigger and Stronger Muscles

The human body consists of 650 muscles and whether you consciously care for a hundred of them or just four, you need all of them to carry out the daily activities of life such as breathing, eating, walking, holding a magazine- you get the gist.

That said, you don’t have to pay much attention to your muscles in order for them to do their job. I mean, you don’t give much thought to the 200 muscles responsible for the walking function but they do their job regardless.

Besides, most people don’t even have the slightest interest in the function of their different muscle groups. You’d probably hear crickets if you were to break out muscle trivia in a cocktail party because telling your friends that the latissimus dorsi in the mid-back area is the largest in the human body doesn’t really capture the amazing wisdom of how muscles work together or the brilliance of strong muscles in isolation.

The following section of this article is aimed at deepening your understanding of how human muscles work and what you can do to get them big and more appealing visually if that’s your goal. In fact, you can realize all three of these objectives if you have background info on how muscles work.

Muscle Fibers Do Different Things

Your skeletal muscles, which are the most visible ones, consist of two types of fibers.

There are type 1 fibers, which are also known as slow-twitch, and are mostly responsible for endurance, while Type 2 or fast-twitch fibers only step in when you’re performing tasks that require more than 25% or more of your total strength. Keep in mind that slow-twitch fibers don’t only step in when you’re performing slow movements, but they take over when the action is below the threshold required for fast-twitch strength. Similarly, you don’t have to be performing a “fast” movement in order to activate fast-twitch fibers.

While doing a PB bench press is not necessarily a fast action, it still requires every ounce of fast-twitch fibers and slow-twitch fibers as well.

It is believed that most people are born with an equal mix of both slow and fast-twitch fibers, with the exception of elite athletes and marathoners, who are probably born with a higher ratio of slow-twitch fibers than fast-twitch ones, while an NFL running back or Olympic champion sprinter probably has more fast-twitch fibers than slow ones. Also, fast-twitch fibers are 2x larger than slow-twitch fibers and can potentially get larger. Slow-twitch fibers also have the potential to grow large, but not to the same degree as fast-twitch fibers.

This makes the strategy very clear then…

To Grow Large, Lift Large

As soon as you start engaging in any activity, whether it’s as simple as turning the page of a book or as complicated as swinging a baseball bat, there are two basic principles that are usually at work:

  • The all-or-nothing principle suggests that a muscle fiber either goes all in on the action or stays put. Once it starts, it goes all in. so even if you’re performing a task as simple as getting out of bed, all the muscle fibers involved in that action are working their butts off to make sure that you get up. Meanwhile, all the other fibers remain inert.
  • The size principle states that it is the muscle fibers that begin a task. So if for example, you’re doing a bicep curl that involves less than 25% of the strength in your biceps, then it’s only the slow-twitch fibers that will get to work. Whereas, if the task at hand has a strength requirement of more than 25% then fast-twitch or Type 2 fibers, have to step in. basically, fast-twitch fibers only get involved when you push yourself to the utmost limits of your strength.

This is important because a lot of people believe in the false notion that exhausting a muscle is enough to summon all its fibers into action, which couldn’t be further from the truth. According to this theory, doing multiple reps using light weights will cause your Type 2 fibers to step in because the type 1 fibers will simply tire out of all the activity.

However, according to the size principle, the biggest fibers only step in when the smaller fibers cannot handle a particular task.

This means that if you want to build a lot of muscle, then you must lift weights that require the maximum amount of effort possible, as that’s what will compel the Type 2 fibers to step in. Plus, the smaller fibers will be fully engaged as well because the size principle shows us that small fibers also get involved in the fight when big fibers are pushed to their limits.

Building Muscles Saves Your Bones

There have been a lot of naysayers that criticize the squat as being too damaging to the knees and back, but none of these criticisms have stuck. Granted, certain exercises like the squat can be quite taxing on the knees, but it is no more difficult to pull off than doing any type of full-bore sports activity.

Plus, the squat is a great exercise for anyone that wants to build strength, improve sports performance, and achieve long-term health and mass. Lifting heavy weights helps to build muscle size and strength as well as bone density, which will come in handy as you age. Thicker bones will protect you from frail hips that break easily, and you’ll finally be glad of all those squats you did when you were young.

Setup: Place a bar in supports whose height is just beneath the shoulders, and position the weights. Start with lighter weights in the beginning if you’ve never done squats before as you’ll have to learn the ropes first. Grasp the bar while making sure that your hands are positioned just outside your shoulder, and then get yourself underneath the bar before resting it on your back. Tug your shoulder blades together to give the bar a resting shelf. Take the bar off from the supports and take one step back. Place your feet shoulder-width apart, engage your abs, get your knees slightly bent, squeeze the glutes and make sure that your head is aligned with the spine with your eyes forward at all times.

Descent: Bend the knees and hips at the same time to commence the squat and lower your body. Try and get a really deep squat, and don’t let your trunk advance for more than 45 degrees from vertical position. Meanwhile, your heels should be firmly planted on the floor.

Ascent: Squeeze the glute muscles and thrust them forward before you begin with the ascent, which should be like the descent in reverse. Make sure to maintain the same distance between your knees, and your shoulders should be moving at the same angle as well because if your hips come up first then you might end up putting unnecessary strain on your lower back. Remember, the knees should be slightly bent the whole time.

You Can Improve Muscle Quality

There are probably three aspects of muscle quality that most of us would probably object to if we could:

  • The maximum number of muscle fibers that you have.
  • The percentages of slow-and-fast twitch fibers that you have.
  • How your muscles get shaped once they’re fully developed.

Truth is, the best athletes in the world, the ones who’re capable of superhuman feats, were actually born with genes that supported their current physical composition, which is what enables their muscles to look and perform as they do.

On the bright side, there is some wiggle room that you can exploit to at least reach your genetic potential. Sure, you won’t become some Olympic-level freak in terms of muscle appearance and performance but if you put in enough work and perform the right tasks then you can get bigger than you are now.

The best route to take in getting there involves utilizing the muscles themselves.

More Muscle Comes from More Testosterone

Pretty much everyone has some level of testosterone, from babies to little girls and even your grandmother, but it’s only the maturing male who experiences year on year increases of this hormone. In fact, between the ages of 9 to 15, his testosterone levels shoot up tenfold and from late puberty onwards, his testosterone levels level out and increase gradually until he hits the age 30, where it starts to ebb and flow a bit.

  • Perform exercises that require the use of lots of muscle mass, i.e. deadlifts, squats, dips, and pull-ups.
  • When training, lifting heavy weights that are, at the minimum, 85% of what you’re capable of lifting.
  • Challenge yourself by doing lots of different exercises during your workout routine.
  • Ensure that rest period are kept short and sweet, 30 to 60 seconds is more than enough between each exercise. However, make sure you switch it up with different workouts every other week not only to keep things interesting but so that you’re able to perform different exercise activities that challenge your body in different ways.

For most men, muscle mass will reach its peak between 18 and 25, that is unless he starts getting in some barbell exercises. Sexual desire tops out during the early 30s while sports performance reaches its peak in the late 20s and begins to steadily decline during the early 30s, and this goes for elite athletes and Olympic performers as well.

Of course, none of this is set in stone, and there’s always a chance that you’ll grow bigger and stronger with time. And you might even be able to reach teenage-level sexual desire again.

The connection between muscle mass and testosterone is generally clear:  When you have a lot of one component, you’ll have a lot of the other as well. While strength training won’t do much to increase your testosterone levels on a permanent basis, it can cause it to spike up a bit on the short-term. The following four methods can be utilized to generate a temporary spike in testosterone.

Muscles Need More than Protein

While the science behind protein and building muscle is quite straightforward, there is no shortage of false theories on the subject. Here’s the skinny: Protein is one of the main components that make up your muscles, ergo, protein is the ideal food to eat if you want to make them grow. Consuming protein also protects your muscles from growing smaller, which is why it’s always a good idea to opt for lean protein like fish, poultry, low-fat dairy products and eggs when you want to lose fat without losing muscle.

That said if you’re young, lanky and attempting to gain weight, consuming more protein might not be the answer. Certain characteristics of protein are actually capable of restricting weight gain while facilitating effective weight loss. First of all, it is very difficult for the human body to process protein, and it needs to burn almost 20% of each protein calorie during the digestion process alone. In fact, your body burns 2% fat and 8% carbs in total during digestion.

Also, protein will fill you up fast and keep you feeling fuller for longer in between meals, but its effects won’t change over time so you don’t have to worry about protein consumption affecting your weight loss goals in the long-term.

Lastly, if you happen to consume more protein than necessary, your body will just use the surplus as energy. That said, you don’t want to do that too often as the human body should ideally depend on burning carbs and fat for energy instead of protein in order to maintain long-term optimal health.

So, if you want to gain weight then you should pay attention to the number of calories you take in first, and then worry about protein after. The protein you consume should ideally make up 2 grams of each kilogram of muscle mass. One kilogram is equal to 2.2 pounds, which means that someone who weighs 160 pounds (73 kg) for example, will need to get a daily intake of 146 grams of protein. That equates to 584 calories worth of protein, which is the same as a 28-ounce steak, two salmon fillets and 15 ounces of chicken. Drinking a protein shake is one of the best ways to boost your protein levels as well, and adding vegetables like a sweet potato on the side is great for weight gain.

Do Deadlifts

A deadlift involves lifting something that weighs significantly more than you do, and if you’ve ever watched one of those Strongman contents on television then you may (or may not) have noticed that most of the guys participating had noticeably round rumps. Yep, barbell exercises will not only increase your strength exponentially, but they’ll also lead to a more attractive shape to your physique as well.

Dip for Big Triceps

Lightweights combined with simple exercises and a limited range of motion is a great start for most beginners. However, if you really want to size up on your triceps, then you should start lifting super heavy loads.

One of the most effective and highly recommended exercises for triceps is the dip. The great thing about the dip is that it allows you to hit three birds with one stone, meaning that it works three different parts of the same muscle. This primes your triceps to lift heavier loads more efficiently than they would if you were only engaging them through a muscle isolating exercise.

Run Less to Grow Faster

As you may already know, running is not the best activity to engage in if you want to build muscle mass. That’s why runners usually have small muscles that enable them to stay light on their feet.

However, some people still think that they can mitigate the effect of running on their muscles by lifting more weights in addition to running, but the body’s “interference effect” negates all that. While the large Type 2 fibers will continue to grow as you combine lifting and running, your Type 1 fiber will stop growing, and since they make up 50% of the of your body’s total muscle fiber count, you can bet that they’ll put a damper in your plans to grow more muscle, regardless of how much you lift in addition to running.


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