The human body has
more than 650 muscles, which make up half of a person's
body weight. They are connected to bones by tough,
cordlike tissues called tendons, which allow the muscles
to pull on bones. The narrow bands on the top of your
hands are tendons; you can see them lengthen and shorten
as they pull on your fingers to make them move. Bones are
fastened to other bones by long, fibrous straps called
ligaments, which wrap around the joints. Cartilage is a
flexible, rubbery substance that supports bones and
protects them when they rub against each other. Together,
bones, muscles, tendons, and ligaments form the
Humans have three
different kinds of muscle - skeletal, smooth, and cardiac.
Skeletal muscles are attached to bone, mostly in the legs,
arms, abdomen, chest, neck, and face. These muscles are
called striated because they are made up of fibers that
have horizontal stripes. They hold the skeleton together,
give the body shape, and help it with everyday movements.
Skeletal muscles can contract (shorten or tighten) quickly
and powerfully, but they tire easily and have to rest
between workouts. Their size varies greatly depending on
the job they do, and they are known as voluntary muscles
because you can control their movement.