What makes muscles grow?

Have you ever wondered how your muscles actually grow? Whether you’re lifting weights at the gym or just opening a heavy door, your muscles are constantly at work, adapting and changing to meet new challenges. But how exactly does this process happen?

Muscles make up a significant portion of our body weight—between one-third and one-half—and are crucial for our movement and stability. We have over 600 muscles, and they, along with connective tissues, bind us together, hold us up, and help us move.

How Muscles Work: Imagine you’re standing in front of a door, ready to pull it open. Your brain and muscles are perfectly poised to help you achieve this goal. First, your brain sends a signal to tiny messengers in your arm called motor neurons. When they receive this message, they fire, causing muscle fibers (think of them as tiny threads that make up your muscles) to contract and relax. This pulling action on the bones in your arm generates the movement you need. The bigger the challenge, the stronger the brain's signal grows, recruiting more muscle fibers to help you overpower the door.

Team Effort: What if the door is made of solid iron? At this point, your arm muscles alone won’t be strong enough to pull it open. So, your brain calls upon other muscle groups for help. You plant your feet firmly on the ground, tighten your belly muscles, and tense your back, generating enough force together to yank it open. Your nervous system has just leveraged the resources you already have—other muscles—to meet the demand.

Muscle Damage and Repair: While all this pulling is happening, your muscle fibers undergo another kind of change. As you expose them to stress by working them hard, they experience microscopic tears, which, in this context, is a good thing! In response, the injured cells release tiny messengers called cytokines that activate your immune system to repair the injury. This is when the muscle-building magic happens. The greater the challenge you place on your muscles, the more your body needs to repair itself. The resulting cycle of damage and repair eventually makes muscles bigger and stronger as they adapt to progressively tougher demands.

Building Bigger Muscles: To build new muscle, a process called hypertrophy, our muscle fibers need to be exposed to challenges that are tougher than they're used to. Everyday activities generally don't push your muscles hard enough to trigger new muscle growth. So, to make your muscles bigger and stronger, you need to continuously challenge them with some resistance, like lifting weights or doing bodyweight exercises. If you don't challenge your muscles, they will actually shrink, a process known as muscular atrophy. Interestingly, exposing the muscle to a high degree of tension, especially while the muscle is lengthening (like lowering weights slowly), creates ideal conditions for new muscle growth.

Nutrition and Rest: However, muscles rely on more than just hard work to grow. Without proper nutrition, hormones, and rest, your body wouldn't be able to repair the tiny tears in your muscle fibers. Protein in your diet acts like Legos for your muscles. You need enough protein (amino acids) to repair the tiny tears and build new muscle fibers, making them stronger. Adequate protein intake, along with naturally occurring hormones like insulin-like growth factor and testosterone, helps shift the body into a state where muscle tissue is repaired and grown. This vital repair process mainly occurs when we're resting, especially at night while sleeping.

Factors Affecting Growth: Gender and age affect this repair mechanism, which is why young men with more testosterones generally have an advantage in muscle building. Genetic factors also play a role in one's ability to grow muscle. Some people have a more robust immune system response to muscle damage and are better able to repair and replace damaged muscle fibers, increasing their muscle-building potential.

The Key to Growth: The body responds to the demands you place on it. If you challenge your muscles with exercise, eat right to provide the building blocks for repair, and get enough rest to allow for repair, you'll create the conditions to make your muscles as big and strong as possible. Just like in life, meaningful growth requires challenge and stress.