Muscles are attached to bones. Muscles usually work in pairs. One will contract — pull the bone in while the second relaxes — releasing the bone. Try it yourself! Look or feel just below the back of your knee. Point your toes. Feel a muscle contract? Straighten your foot. The muscle relaxes.

How Many? Some muscles move like the muscles in your hand. Other muscles move involuntarily — without you thinking about them at all like the muscles in your heart which pump blood. Muscles make up 40 percent of your body’s weight — almost half!

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