Muscles make up between one-third to half of our body weight. Along with connective tissue, we have over 600 muscles in our bodies that help bind us together, hold us up, and help us move. Our muscles need constant attention because the way we treat them on a daily basis determines whether they will wither or grow.
Let’s look at this example. You are 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 the motor neurones inside your arm. When they receive this message, they fire, causing muscles to contract and relax, which pull on the bones in your arms and generate 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 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 open the door. In doing so, your nervous system has just leveraged the resources you already have in your body – other muscles – to meet the demand.
While all this is happening, your muscle fibres undergo another kind of cellular change. As you expose them to stress, they experience microscopic damage, which in this context, is a good thing. When this damage occurs, the injured cells release inflammatory molecules in response, which are known as cytokines. These molecules 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.
Since our bodies have already adapted to most every day activities those generally don’t produce enough stress to stimulate new muscle growth.
Hence, in order to build new muscles, 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. This is known as muscular atrophy.
In contrast, exposing the muscle to high-degree tension, especially while the muscle is lengthening (also called an eccentric contraction), generates effective conditions for new growth.
Muscles rely on more than just physical activity for growth. Without proper nutrition, hormones and rest, your body would never be able to repair the damaged muscle fibres. This is where protein plays a role.
Protein in our diet helps preserve muscle mass by providing the building blocks for new tissues in the form of amino acids.
Adequate protein intake, along with naturally occurring hormones, help shift the body into a state where tissue is repaired and grown. This important repair process mainly occurs when we are resting, especially at night while we are sleeping.
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Gender and age affect this repair mechanism. Genetic factors also play a role. Some people have a more robust immune reaction to muscle damage and are better able to repair and replace damaged muscle fibres, 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 needed to make your muscles strong.
It is with muscles, as it is with life. Meaningful growth requires challenge and stress.
(Adapted from TED-Ed by Jeffrey Siegel)