Machine Leg Extension Exercise Guide

A leg workout is not complete without a few hard-fought reps on the leg extension machine. Leg extension isolates the quads – one of the biggest muscle group in your body – and can produce outstanding definition in your thighs. Quads work to straighten the knees, so this exercise can help protect your knees or assist with rehabilitation after a knee injury. A leg extension machine can work each leg individually or both legs together. This is one of the few exercises where it may be better to alternate work on the two sides rather than doing both together. In this post you will find out how to perform machine leg extension exercise safely efficiently.

Machine leg extension proper technique

Here are detailed instructions on how to perform machine leg extension exercise safely and effectively to achieve maximum results from this great quadriceps exercise.

STARTING POSITION (SETUP): Select a weight from the stack and adjust the back of the seat so that the axis of the machine is in line with your knees. Adjust the shin pad so that it is just above your ankles. You can usually adjust the back pad and foot pad to obtain the desired position. Your knees should be bent 90 degrees or more, with your toes pointing in front of you. Grasp the handles firmly, with your torso upright, your back against the pad, and your hips pulled down securely into the seat.

Machine leg extension

MOVEMENT (ACTION): Grab the handles on either side of the seat for support – to keep your hips from lifting up. Tighten your abdominal muscles to help protect your back. Raise your lower legs up (extend your knees) in a semicircular motion until your legs are straight (but not locked) and can’t go any higher. In other words, your legs should be parallel to the ground at the top of the movement. Your toes are pointing directly upward during the movement. Pause for a second in the contracted position before lowering the weight down slowly to the starting position.

Machine leg extension tips & key points

There are some tips that will help you get even more out of this already amazing quadricep exercise.

Look for only your lower legs to move: the entire rest of your body should remain stationary.
Don’t let your back move forward or your buttocks come off the seat during the movement.
Be sure that your thighs, lower legs, and feet are parallel to each other.
Avoid allowing any space between the back of your knees and the seat edge.
Avoid any spinal movement whatsoever.
Control the movement in both directions.
Avoid elevating your shoulders.
Avoid allowing your hips or gluteals to elevate off the seat.
Do not arch your back or raise your hips off the seat to help you lift the weight.
Maintain an upright torso – right against the seat back.
Never “kick” up the weight up in a jerky manner. Make sure you maintain a constant motion during the entire exercise.
Do not turn your toes in or out. Keep your feet straight as you perform the exercise.

Exercise video demonstration

This short instructional video will demonstrate you how to perform leg extension exercise using perfect technique so you can get maximum results.

Leg extension variations

One-leg extension. This variant is identical to the basic exercise, but the legs are worked alternately. You can either do a whole set on the same leg or alternate repetitions (this is easier because of the short rests). Performing this exercise one leg at a time improves focus. The unilateral leg extension is particularly useful for improving thigh asymmetry or aiding in rehabilitation when one leg is injured. It also prevents the stronger leg from helping the weaker one, which can happen in the basic exercise, as machines tend to be poorly designed for working both legs at the same time.

Another helpful technique is to vary leg/foot position. These variations create different recruitment patterns for muscles, thereby producing the most complete workout possible for the leg extension. For example, turning your feet (toes) slightly out (targeting the vastus medialis) or slightly in (targeting the vastus lateralis) will work the quads in a functionally different way. Pointing your toes directly upward hits all sections of the quadriceps equally.

Try this exercise while holding a soccer ball between your knees to put extra emphasis on the vastus medialis.
Machine leg extension with short arc. If you have a history of knee pain, limit your range of motion in the flexion phase of this exercise. The leg extension with short arc is an excellent exercise for developing quadriceps strength in the presence of knee pain due to patellofemoral syndrome. The only drawback is that it is not involve the full range of motion; however, once the knee pain dissipates, the full-extension version of the exercise can be performed.

Muscles involved in machine leg extension

Main muscles: quadriceps (vastus internus, externus, intermedius)
Secondary muscles: front quadriceps, gluteal deltoid (tensor fasciae latae and superficial fibers of the gluteus maximus)
Antagonists: hamstrings, biceps femoris (short head), gracilis, sartorius, gastrocnemius

Replacement exercises

There are a lot of opinions about how to best train your quadriceps. We’ve assembled the ten best-rated strength exercises for quadriceps from our database, along with tips from the experts.

Closing thoughts about machine leg extension exercise

Machine leg extension focuses on your quadriceps and is one of the best ways to develop strong and defined thighs. In addition to giving you stronger and more toned thighs, the machine leg extension helps strengthen your knee joints. To ensure that you get the most out of performing this exercise, you should try to complete the full range of motion by raising the weight all the way up (until the knees are just short of being locked) and lowering the weight all the way down. You should also make sure you concentrate on performing the movements slowly.

To prevent injuries, avoid jerking your legs up rapidly or locking your knees at the top of the movement.
You should also avoid using more weight than you can control. If you are using too much weight, you may have a tendency to inadvertently slam the weight down onto the stack between repetitions.