Shayne Culpepper is a fine example of a runner who keeps their feet low during their stride. This is accomplished by relaxing all the leg muscles after toeoff (except the hip flexor) and simply pulling the knee forward. The lower leg flexes naturally at the knee then flips forward to extend the knee again. The hamstring (primarily) is used to brake the foot again before touchdown.
Note how Shayne doesn't wait to begin bringing the foot forward after toeoff. Other great runners who do this are Hicham El Geurrouj, Sebastian Coe, and Alan Webb.