How Muscles Grow: The Science Behind Your Gains

Ever wonder what’s really happening when you’re lifting weights and your muscles start to grow? Let’s break it down and give you the upper hand with science backed information.

The Basics of Muscle

First things first—when we talk about muscles growing, we’re focusing on your skeletal muscles. These are the muscles you control voluntarily, like when you decide to lift a weight or go for a run. Unlike the smooth muscles found in places like your stomach or blood vessels, skeletal muscles are all about movement and strength.

Now, let’s get into what makes a muscle special. Unlike most cells in your body, which are small and round and have a single nucleus, a muscle cell is long and cylindrical—about the size of a human hair! These cells, called muscle fibres, are packed with nuclei that act like tiny control centres. These nuclei manage different sections of the muscle, helping it perform at its best.

How Muscles Create Force

When you lift a weight, your brain sends a signal to your muscles, telling them to contract. This contraction is powered by something called actin-myosin cross-bridges, which are like little hands inside the muscle fibres that grab onto each other and pull. The more cross-bridges formed, the more force your muscle produces.

The brain organises this effort through what’s known as motor units—a motor neuron and the muscle fibres it controls. Depending on the size of the motor unit, it might control a few or many fibres along the entire muscle. Smaller motor units are great for endurance tasks (like running), while larger motor units are used for heavy lifting but get tired more quickly.

Why Muscles Grow

So, what actually triggers muscle growth?

It all comes down to the tension in your muscles. When you lift heavy weights, your muscles experience a lot of tension, which signals your body to start adapting. This adaptation involves the growth of muscle fibres, making them bigger and stronger to handle the load better next time.

The Role of Chemical Signals

When you put stress on your muscles, they start a process called mechanotransduction—where a physical force is converted into a chemical signal. This signal tells your muscles to release growth factors and other chemicals that help repair and build muscle tissue.

One key player in this process is an enzyme called mTOR. This “master switch” helps regulate muscle growth by responding to signals like nutrient levels and energy availability. When mTOR gets the go-ahead, it tells your muscle cells to start building more muscle.

 Adding More Nuclei

As your muscles grow, they need more nuclei to manage the new muscle fibres. These extra nuclei come from satellite cells, which are like backup cells waiting to jump into action. When your muscle fibres get damaged, these satellite cells fuse with the muscle fibres, adding their nuclei to help manage the extra workload. This is one of the proposed reasons that muscle memory exists (when you re-gain strength and size very quickly after taking time off). It’s proposed that this occurs because the additional satellite cells your body made when you were training are still present and available to control more muscle.

Muscle Damage and Recovery

You’ve probably heard that you need to “feel the burn” to grow muscle. That burn is caused by metabolic stress, which is just one way your body signals it’s time to grow. However, recent research suggests that muscle damage and soreness (like DOMS—Delayed Onset Muscle Soreness) aren’t the main drivers of muscle growth. In fact, too much damage can actually slow down your progress by delaying recovery.

Instead, the real magic happens when your muscles experience mechanical tension. This tension, caused by exercise, is the primary trigger for muscle growth. So while a little soreness is normal, you don’t need to chase that feeling to see gains, and if you don’t feel the burn this doesn’t mean you aren’t also growing muscle.

Strength vs. Size

While muscle size and strength are related, they’re not the same thing. Your muscle size is like the engine of a car, and your nervous system is the driver. Both need to work together to improve your performance.

When you train, your muscles adapt by repairing damaged fibres and adding new ones. This process not only makes you stronger but also increases your muscle size, especially if you’re using progressive overload and constantly providing a stimulus to your muscles as they get stronger.

References

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