Leg extension

Leg extension

The leg extension is a resistance weight training exercise that targets the quadriceps muscle (m. quadriceps femoris) in the legs. The exercise is done using a machine called the Leg Extension Machine. There are various manufacturers of these machines and each one is slightly different. Most gym and weight rooms will have the machine in their facility. The leg extension is an isolated exercise targeting one specific muscle group, the quadriceps. It should not be considered as a total leg workout, such as the squat or deadlift.

How to perform

Setup

Align the backrest to support a straight posture and adjust the seat so that your knees align with the fulcrum. Align the lower moving pads so that they rest against the front of your shin. The upper support pad should be lowered until it places gentle pressure on your thighs.

Setup without a machine

Sit on the edge of a stable and flat bench/chair. While holding onto the sides of the seat with your hands, extend one leg outward to a straightened or slightly bent position. Hold that position for 1-2 seconds and reset to the starting position. Repeat on the same or other leg and complete repetitions for the set. The goal is resistance in your quads building throughout the sets, holding for a longer time or adding different forms of resistance to build strength.

Movement

Initiate the movement by extending your legs up against the moving pad, raising the weight until your legs are parallel to the ground. Then, slowly lower the weight in a controlled manner while bending your knees until you return to the initial position.

Common mistakes

Common mistakes to avoid while performing the exercise include Incorrectly setting up the machine. Not adjusting the machine to fit your body is a common error that can lead to feeling uncomfortable, slowing your progress, and injury risk. Another common mistake is an incomplete range of motion. Setting up the machine at 90 degrees and then pressing your legs up to 45 degrees is the recommended range of motion. Another common mistake is using too much weight. Using more weight than you can handle can lead to using body momentum, which will hurt your results and place unnecessary strain on your joints.

Variations

Can be used with a weight bag or resistance band attached to the user’s ankle on the leg in use to increase the difficulty and strengthen quadricep muscles.

Muscular Engagement

Photo of student using leg extension with pad and seat angled back.

The exercise consists of bending the leg at the knee and extending the legs, then lowering them back to the original position. The exercise engages all four heads of the quadriceps. These heads consist of the vastus lateralis, vastus intermedius, vastus medialis and rectus femoris. The vastus lateralis has been shown to engage more during the movement when toes are pointed inward. The rectus femoris engages more when the toes are pointed outward. Research has shown, that performing the leg extension with the hip flexion at a 40-degree angle rather than the typical 80-degree angle can promote more rectus femoris activation. This is because the rectus femoris attaches to the hip, and leaning backward stretches the muscle more. Additionally, angling the arm of the machine closer to the seat places your quad muscles in a more stretched position, potentially causing more muscular growth. However, if this position is uncomfortable, please adjust the arm of the machine to the most comfortable angle.

What the exercise is used for

The leg extension exercise is for different purposes in many different workout routines.

Runner's training

The quads are an extremely important muscle to train when excelling in running and most sports. Leg extensions are a great exercise to isolate the quadriceps. Leg extensions can be performed to maximize endurance and hypertrophy (mid-high rep ranges) or explosive strength (mid-lower rep ranges).

Physical therapy

In a physical therapy context, patients can perform leg extension variations to build muscular quad strength. Many physical therapists use this exercise to help patients rehabilitate after knee surgery and to address knee pain. Many physical therapists refer to leg extensions as Long Arc Quads and Short Arc Quads. Long Arc quads are similar to the leg extension exercise described in this article. Patients sit at the end of a bench or platform, placing their knees at a 90-degree angle. The patient then extends their leg and then slowly lowers back down to 90 degrees. Short Arc Quads are variations performed by laying the leg flat and then placing an elevated platform under the knee. Then extending the elevated knee to perform a shorter range of motion leg extension.

Risk of injury

Some fitness professionals and coaches advise against using an isolating leg extension machine because they believe it puts unnatural pressure on the knees and ankles.. However, this concern is based more on anecdotal evidence than on solid research. Whilst there is some evidence that the leg extension's unnatural moment arm places constant tension on the anterior cruciate ligament (ACL), there is no proof that this increases the risk of injury, except for those with pre-existing ACL issues. The leg extension is a good exercise for isolating muscular contraction in the quadriceps, but as with all isolation exercises, should be included in a holistic resistance training program working all muscles, especially antagonistic muscle pairs (such as the quadriceps, hamstrings, and gluteal muscles), to avoid muscular imbalances, which are associated with increased injury risk.

History

The leg extension machine was created by American fitness guru Jack LaLanne in the 1950s. The first prototype is recognized to have been made under Gustav Zander, but labeled the machine as a form of “mechanotherapy” along with other machines that extended the knee and ankle. The machine was made to target the quadriceps. The exact method of inventing the leg extension machine is not consistently recorded, but in most cases, it is attributed to LaLanne.