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Muscle in on Muscles

Your muscles move you!

Meet your muscles. This activity lets you know about kinds of muscles, how you use them, and what happens to them in space.

Front and back view of the muscles of the human body. Muscles are labeled and lines are drawn from the label to the muscle.

Muscle up Facts

drawing of a flexing bicep muscle of the arm

Voluntary and Involuntary are the two types of muscles in your body.

You have direct control over voluntary muscle.

You cannot make involuntary muscle contract and move through conscious control; its movement is automatic.

Let's take a closer look at each type of muscle.

Voluntary Muscle

image of the spine

Voluntary means chosen or optional, so you decide when to use these muscles.

Postural, or anti-gravity, muscles are a type of voluntary muscle. Postural muscles include:

These muscles are loaded with weight in the Earth's gravity, allowing you to walk, run, and stand up straight.

skeletal muscle attached to bones

Skeletal muscle is voluntary muscle. You control the movement of your bones.

Skeletal muscle is typically attached to bones by tendons, a string-like tissue.

Skeletal muscle contracts to move the bone with the muscle.

Involuntary Muscle

Involuntary means uncontrolled or automatic, so you have no direct control over your involuntary muscles.

These muscles work with or without gravity.

Cardiac and smooth muscle are the involuntary muscles.

image of human heart

Cardiac muscle is related to the heart.

This muscle keeps blood pumping through the body.

image of intestines

Smooth muscle is found in the iris of the eye and in your intestines, among other places.

Smooth muscle moves food through the organs of your digestive system without gravity being necessary.

Astronauts are able to eat and digest food in space.

Muscles in Space

photograph of an astronaut using the exersise bike in space

Muscle must be constantly stimulated in order to maintain strength. Some muscles are stimulated (or work harder) because of the presence of gravity and its corresponding resistance.

If you've visited the Muscle Up Facts link yet, you know these are voluntary, or anti-gravity, muscles. These muscles create movement that opposes the gravitational pull of the earth.

photograph of an astronaut floating inside the ISS

With gravity here on Earth, these muscles are constantly at work and remain strong. However, because they don't have to resist the gravitational pull of the Earth while in space, muscles atrophy, or decrease in size.

As muscles decrease in size they lose strength.

For example, instead of using leg muscles to walk or run, astronauts float effortlessly, not using their muscle power very much.

With daily weight training, astronauts counteract some changes and atrophy in their muscles. Scientists and doctors work to develop countermeasures so that humans will be able to work and live in space for long periods of time.

Muscle atrophy research in space also helps doctors treat people who:

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