MUSCLES YOU ARE WORKING OUT. You’re working out all four parts that make up the quadriceps, i.e. the muscle that occupies the front part of your thigh. It’s made up of: vastus lateralis (outer part of the thigh), vastus medialis (the “teardrop”), vastus intermedius (central area) and rectus femoris (along the front thigh). They are inserted into the patella through a common tendon and then inserted into the tibia. These muscles are monoarticular, except for the femoral rectum, which is biarticular and acts on the knee extension and the hip flexion.
HOW TO PERFORM THE EXERCISE. Sitting on a Leg Extension machine, resting your thighs against the seat and your back on the backrest, holding on to the lateral edges (or handles) with your hands. Your knees should be leaning just over the end of the seat with your feet supported under the roller. From this initial position, contract your quads so as to raise your calves till they’re aligned with your thighs, tightening those muscles. Then go slowly back down to the starting position, without dropping the roller. Repeat this movement as many times as necessary.