Which muscles are antagonists to the hamstrings? in complex movements, muscles commonly work in groups rather than individually. the hamstrings flex the knee. which muscles are antagonists to the hamstrings?

Agonist muscles and antagonist muscles are the muscles that cause or inhibit a movement. Agonist muscles cause a movement to occur through their own activation, whereas antagonist muscles produce an opposite joint torque to the agonist muscles controlling the movement.  

Hamstrings are the group of the muscles and tendons located in the upper leg. They include the biceps femoris, semimembranosus and semitendinosus which play an important role in walking, running and jumping. They bend the knee and move hip backward. The muscle that is antagonist to the hamstrings are the quadriceps. Quadriceps are the group of muscles located in the front of the thigh which include the vastus lateralis, vastus medialis, vastus intermedius and the rectus femoris. They help in extending or straightening the knee. Hamstrings contract to bend the legs and the quadriceps relax. Quadriceps contract to straighten the leg and the hamstrings relax.