The quadriceps, also known as the thigh muscles, move the knee and the hip, and they prevent the knee from buckling. The quadriceps are engaged when doing squats, climbing stairs, standing up and walking.
The quadriceps completely cover the femur, the medical term for the thigh bone, and are among the strongest muscles in the body. While other muscles cause the knee to bend, the quadriceps are the only muscles that extend the knee. The quadriceps consist of four major muscles: the rectus femoris, the vastus medialis, the vastus lateralis and the vastus intermedius. Kenhub states that the quadriceps are uniquely prone to shortening and should be stretched regularly.