TedEd: What makes muscles grow?

A TedEd by Jeffrey Siegel

There are over 600 muscles in our body that hold us together and allow us to move. Most people know that the way you treat them on a daily basis determines whether they grow or shrink. Muscles work by receiving electrical signals from the brain via neurons, which causes them to contract or loosen. If a task is harder, the brian puts more muscles to use. With most everyday tasks, your muscles experience easy loads. But when it encounters a difficult task, the muscles strain, causing microscopic damage. This might sound bad, but it's actually how muscles grow. Your immune system deploys cytokines to the damaged area to rebuild the muscle, causing that muscle to grow. When your muscles are not exposed to consistent strain, they shrink in a process called muscular atrophy. Putting your muscles in high tension, especially when they are lengthened (eccentric contraction) causes them to grow. In addition to exercise, muscles need rest and nutrition to grow. They need proteins you consume with your food, as well as hormones like testosterone that encourage growth. There are also genetic factors because some people have a more robust immune system to facilitate muscle growth.