Leg Extension Exercises Focus on Which Muscle Region of the Body?

Execution

Leg extensions are typically performed seated in a special lever machine or standing using a cable machine. For the lever exercise, you sit on the chair with your back against the padded back rest. Adjust the seat so that your knees are at the edge of the seat. Place the front of your shins under the padded lever pad and hold on to the hand bars for support. Exhale and slowly raise your legs until they are fully extended in front of you. Pause briefly and return to the starting position on the inhale. For the standing variation, place one of your legs in a cable boot strap attached to a low cable pulley. Bend your knee, bringing your heel close to the pulley source. Hold on to something in front of you for support and slowly straighten your leg, bringing it slightly in front of you. Pause briefly and bend your knee to return to the starting position.

Muscles Used

The seated exercise isolates the quads because it only requires you to bend and straighten your knees. Your traps and levator scapulae in your shoulders and neck are worked to a much lesser degree, as they are used to stabilize you as you move your legs. The standing exercise also focuses on your quadriceps, but it strengthens your iliopsas and tensor fasciae latae in your hips and your sartorius, or inner thigh, as well. These muscles serve as synergist muscles and assist the quadriceps in the exercise. Your abs and glutes also get a bit of a workout as they stabilize your body throughout the exercise.

Effectiveness

Although the leg extension has been proven to strengthen the quadriceps, it is not necessarily the most effective exercise for this muscle group. A study published in the February 2000 issue of Medicine and Science in Sports and Exercise found that the leg extension is similar to the leg press exercise in its ability to strengthen the quadriceps. A more recent study published in September 2001 in the same journal, however, found the leg press, which had already been proven to be similar to the leg extension, wasn't as effective as a simple squat.

Precautions

Use the leg extension machine as part of an all-around leg-training program, including different quadriceps, hamstrings and calf exercises to make sure you get an effective lower-body workout. Different exercises will target your muscles from different angles, keeping them challenged and growing. Rest is almost as important as exercise when you are trying to build muscle, so make sure you leave at least 48 hours between working the same muscle groups to allow them to recover and grow.