Pop Quiz: What's the Function of the Hamstring? Everyone gets: Knee Flexion. Everyone forgets: Hip Extension That's right, the hamstring(s) (3 of the 4) cross 2 joints. The Semitendinosus, and both heads of the Biceps Femoris (long and short) cross both the knee and the hip. So What the Hell Does That do With What?  This means the hamstrings are not only involved in knee flexion, bending your knee, bringing the heel to the butt, like in a seated hamstring curl. The hamstrings are also a player (albeit should be secondary to our old friends the glutes) in hip extension. "The hamstrings have a large moment arm for hip extension, making them a key … [Read more...]