Which muscle group is primarily responsible for extension of the knee?

The quadriceps muscle group is primarily responsible for the extension of the knee. This group comprises four muscles: the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. When these muscles contract, they pull on the patellar tendon, which then causes the knee joint to extend, enabling movements such as standing up from a seated position, kicking a ball, or climbing stairs.

In contrast, the hamstrings, located on the back of the thigh, are primarily responsible for knee flexion rather than extension. The gastrocnemius, a calf muscle, also plays a role in knee flexion and works primarily during movements that involve the ankle. The deltoid is a shoulder muscle, which has no direct function related to the knee joint. Understanding the specific roles of these muscle groups is crucial for physical therapy technicians as they assist in rehabilitation programs targeting specific movements or injuries.