What Makes Muscles Grow

This lesson teaches the science behind muscle growth and how the body responds to the demands we place on it. It covers the basics of how muscles function, how they repair and grow, and the importance of proper nutrition, hormones, and rest in the muscle-building process. It also notes other factors that can play a role in muscle growth, such as genetics and age.

Comprehension Questions

Article

Muscles

We have over 600 of them. They make up between 1/3 and 1/2 of our body weight, and along with connective tissue, they bind us together, hold us up, and help us move. And whether or not bodybuilding is your hobby, muscles need your constant attention because the way you treat them on a daily basis determines whether they will wither or grow.

Muscular Function

Say 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 motor neurons inside your arm. When they receive this message, they fire, causing muscles to contract and relax, which pulls on the bones in your arm and generates the needed movement. The bigger the challenge becomes, the bigger the brain’s signal grows, and the more motor units it rallies to help you achieve your task. But what if the door is made of solid iron? At this point, your arm muscles alone won’t be able to generate enough tension to pull it open, so your brain appeals to other muscles for help. You plant your feet, tighten your belly, and tense your back, generating enough force to yank it open. Your nervous system has just leveraged the resources you already have, other muscles, to meet the demand.

Muscular Damage and Repair

While all this is happening, your muscle fibers undergo another kind of cellular change. As you expose them to stress, they experience microscopic damage, which, in this context, is a good thing. In response, the injured cells release inflammatory molecules called cytokines that activate the immune system to repair the injury. This is when the muscle-building magic happens. The greater the damage to the muscle tissue, the more your body will need to repair itself. The resulting cycle of damage and repair eventually makes muscles bigger and stronger as they adapt to progressively greater demands.

Muscular Growth

Since our bodies have already adapted to most everyday activities, those generally don’t produce enough stress to stimulate new muscle growth. So, to build new muscle, a process called hypertrophy, our cells need to be exposed to higher workloads than they are used to. In fact, if you don’t continuously expose your muscles to some resistance, they will shrink, a process known as muscular atrophy. In contrast, exposing the muscle to a high degree of tension, especially while the muscle is lengthening, also called an eccentric contraction, generates effective conditions for new growth.

Muscular Health

However, muscles rely on more than just activity to grow. Without proper nutrition, hormones, and rest, your body would never be able to repair damaged muscle fibers. Protein in our diet preserves muscle mass by providing the building blocks for new tissue in the form of amino acids. Adequate protein intake, along with naturally occurring hormones, like insulin-like growth factor and testosterone, help shift the body into a state where tissue is repaired and grown.

Muscular Repairs

This vital repair process mainly occurs when we’re resting, especially at night while sleeping. Gender and age affect this repair mechanism, which is why young men with more testosterone have a leg up in the muscle-building game. Genetic factors also play a role in one’s ability to grow muscle. Some people have more robust immune reactions to muscle damage and are better able to repair and replace damaged muscle fibers, increasing their muscle-building potential. The body responds to the demands you place on it. If you tear your muscles up, eat right, rest and repeat, you’ll create the conditions to make your muscles as big and strong as possible.

Vocabulary

muscle – a bundle of fibrous tissue that has the ability to contract and produce movement in the body
Example: Regular strength training is essential for maintaining muscle mass.

connective tissue – tissue that connects and supports other body tissues
Example: Injuries to connective tissue, such as tendons and ligaments, can limit movement.

motor neuron – a nerve cell that carries signals from the brain to the muscles to initiate movement
Example: My motor neuron sent a signal to my bicep to contract, lifting the weight.

contraction – the process of a muscle becoming shorter and tighter
Example: The contraction in my abs helped me maintain proper form during a plank exercise.

inflammation – the body’s response to injury or infection, characterized by redness, swelling, and pain
Example: Inflammation in my elbow joint was causing discomfort during tennis practice.

cytokines – small proteins that are released by cells and play a role in the immune response
Example: Cytokines released by my injured cells activated my immune reaction to repair the damage.

hypertrophy – the increase in size of an organ or tissue due to the enlargement of its component cells
Example: My muscles underwent hypertrophy after a consistent weightlifting routine.

atrophy – the reduction in size or wasting away of an organ or tissue
Example: Inactivity caused the atrophy of the muscles in my legs.

eccentric contraction – a type of muscle contraction where the muscle lengthens while still exerting force
Example: The eccentric contraction of my quads during a leg press helped target different muscle fibers.

protein – a nutrient essential for the growth and repair of the body’s tissues
Example: I made sure to consume enough protein in my diet to preserve my muscle mass.

amino acids – the building blocks of proteins
Example: The essential amino acids in the chicken I ate helped repair my muscle fibers.

insulin-like growth factor – a hormone that plays a role in growth and cell division
Example: The insulin-like growth factor in my body played a role in muscle growth and cell division.

testosterone – a male sex hormone that plays a role in muscle growth
Example: My testosterone levels were higher than average which helped in muscle repair and growth.

immune reaction – the body’s response to foreign substances or invading organisms
Example: My immune reaction helped me to recover more quickly from the muscle damage caused by exercise.

muscle fibers – the individual cells that make up a muscle
Example: Each muscle is made of muscle fibers, which when damaged through workout, needs repair.

muscle damage – the tearing of muscle fibers as a result of exercise or injury
Example: I had muscle damage on my left arm from overuse, so I rested to let it repair.

muscle-building – the process of increasing muscle mass and strength
Example: Regular resistance training and proper nutrition helped me to focus on muscle-building.

muscle-wasting – the process of losing muscle mass and strength
Example: Due to my sedentary lifestyle, I had muscle wasting, which made me weaker.

robust – strong and healthy.
Example: The robust immune reaction helped my muscles to recover faster from the damages caused by weightlifting.

Discussion Questions

  1. How does your daily routine affect your muscle health?
  2. What are some ways to increase muscle growth?
  3. Can you explain the process of muscle repair and how it relates to muscle growth?
  4. How does nutrition play a role in muscle health?
  5. Can you discuss the importance of rest in muscle repair and growth?
  6. How do hormones affect muscle growth?
  7. How do genetics play a role in one’s ability to build muscle?
  8. Can you explain the difference between muscle atrophy and hypertrophy?
  9. How do gender and age affect muscle repair mechanisms?
  10. In what ways can you incorporate resistance training in your daily routine to promote muscle growth?