A leg extension machine isolates the quadriceps through a knee-extension movement. Users sit with ankles behind the roller pad and extend the knees to lift the weight. This single-joint exercise is excellent for pre-exhausting the quads or adding volume after compound lifts. Adjustable backrest and roller positions accommodate different limb lengths for precise, comfortable training. It is often used in rehabilitation to strengthen the quadriceps after knee injury. Bodybuilders use it to shape the front of the thighs and create a more defined sweep above the knee.