How Humans Are Able to Move

In Ways We Don’t Even Realize, Muscles Make Our Bodies Work

by Virginia Quach, age 12

Every move you make depends on muscles, even when these movements go unnoticed.
There are two types of muscles in your body, involuntary and voluntary muscles. Without muscles or oxygen, you wouldn’t be able to move. Involuntary muscles work automatically. They are muscles like the ones around your heart and guts. Voluntary, or skeletal, muscles are muscles you control like those in your arms and legs.
Muscles are bundles of fiber that can tense and relax. They make up 40 percent of your body weight. They need oxygen in order to burn sugar. Most muscles come in pairs. These work by getting shorter, pulling two points together, then relaxing. The flexor is used to bend or flex a joint and the extensor is used to straighten the joint again.
Most skeletal muscles are made of thin strands called myofibrils. On the sides of the myofibrils are stripes called striations. Striations are two alternating substances called myosin and actin. When the actin and myosin pull together, they can shorten the muscle by half. Smooth muscles contract blood vessels to control the blood flow through the guts. That is how food is transferred from your mouth to your stomach.
There are also red and white muscles. These muscles allow you to make movements. The slow-twitch muscle is red. It is good for gentle movements.  White muscles are for fast and powerful movements, like sprinting. Fast-twitch muscles are red and can do fast or slow movements.
Without your muscles, you wouldn’t be able to see, walk, talk, or even run. Muscles are what make it possible for you to do the things you do.

[Source: Simpson Street Free Press]