Leg extensions are a key exercise in strengthening the patellar ligament and the quadricep attachment for the knee. This exercise focuses on strengthening the quad alone and, therefore, strengthens key attachments for the knee joint at the same time. Other leg exercises, such as squats, step-ups and leg presses, work the quadriceps, but the hamstrings, calves or glute muscles assist the during the movement. If your quadriceps are weak, performing leg extensions allows you to focus on strengthening just that muscle. Keep the knees slightly bent and avoid excessive weight to minimise ligament damage. One of my favorite exercises for injury prevention.