This video shows some people overstriding. You can see their quad flex as their knee locks completely out then they heelstrike. Looks very damaging.
"While living I want to live well." - Geronimo
"Video of a series of runners filmed at 300 frames/sec near the ~17.5 mile mark of the 2010 Boston Marathon (on Washington St. near the intersection with Commonwealth Ave.). All were on a sub-3:00 marathon pace at this point in the race. Note the barefoot runner near the middle of the clip. Courtesy ofhttp://www.runblogger.com".