Walking lunges set up the body fantastically for hamstring hypertrophy. The quads are working with every step, as they are in squats, but in this exercise the hamstrings are easy to isolate. The dynamics of lunges are similar to those of squats in terms of lowering the weight. While lowering the weight, strive to sit back as far as possible (like you would with box squats, or if you were going to sit in a chair) awhile maintaing the tension on the front leg, rather than bending the back forward. If the back leg was invisible, the lunge would almost look like a squat where you only see 1 leg. This reduces the pressure on the knee, lower back and on the quads, thus better isolating the hamstrings and calves (although calves are primarily stabilizing muscles in this exercise). Come up by squeezing the hamstrings of the front leg tightly, which should look like you are pushing through the heel of your front foot (like in squats).

I have found that the smoother the eccentric portion is performed, the more forceful the concentric portion can be. When I do lunges, I go down as slowly as necessary to feel the hamstrings controlling the movement and to be completely balanced. The better I control the lowering of the weight, the faster and more powerfully I can push it up. This applies to all resistance exercises, yet it significantly more prominent in leg movements.