1.  You have all the muscle fiber you will ever have at birth.  Once damaged they can’t be replaced.
2.  Arnold Schwarzenegger has as many muscle fibers as you – They’re just thicker!
3.  A single muscle cell of the sartorius muscle in the thigh can be more than 12 inches long.
4.  There are more than 600 voluntary muscles in the body.
5.  The strongest muscle of the body is the masseter muscle used for chewing!
6.  Your hand contains 20 different muscles.
7.  If all your muscles could pull in one direction you could create a force of 25 tons!
8.  Muscles account for approximately 40% of your body weight.
9.  It takes 17 muscles in your face to smile, but it takes 43 muscles to frown.
10. You take approximately 5 million steps per year using your leg muscles!

These facts were found using the link below.
http://tanyastroh.wordpress.com/2009/05/18/10-fun-facts-about-your-muscles/