Yes, and knee extension would be when the knee is straight.
An agonist muscle is a muscle that plays a part in the extension of a muscle. The agonist muscles for a knee extension are the quadriceps and hamstrings.
Vertebral Foraminal Entrapment on Hip Flexion and Knee Extension
The antagonists would be those muscles that cause knee flexion. Hamstrings (biceps femoris, semimembranosus, semitendonosis) are the primary knee flexors, and would thus be antagonists to knee extension.
knee extension
Knee extension
Extension. Extension increases an angle, as in straightening a joint. During extension, the knee or elbow are straightened.
OBTURATOR
iliopsoas
quadraceps
Flexion, extension, rotation, adduction of the hip, extension and rotation at the knee
Flexion, extension, rotation, adduction of the hip, extension and rotation at the knee