THE BODY HUMAN
'(<a href="http://www.j-archive.com/media/2008-06-23_DJ_19.jpg" target="_blank">Jimmy of the Clue Crew gives a physical demonstation.</a>)  Muscles work in pairs, so you can strengthen one by increasing flexibilty in the other. The hamstring curl strengthens the <a href="http://www.j-archive.com/media/2008-06-23_DJ_19a.jpg" target="_blank">hamstring</a> and allows <a href="http://www.j-archive.com/media/2008-06-23_DJ_19b.jpg" target="_blank">this muscle</a> at the front of the thigh to elongate'
the quadriceps