The leg extension is a weighted exercise primarily performed with the aid of a leg extension machine wherein a padded roll is placed against the groove of your ankles and provides adjustable resistance in order to induce muscular hypertrophy in the quadriceps femoris muscle group.
Primarily, the leg extension is considered an isolation exercise owing to the fact that it mostly targets the quadriceps alone, and largely does not require the use of other muscle groups that would normally come into play when performing other kinds of leg exercises.
Fortunately, many alternatives exist to the leg extension exercise, some of which provide similar isolation-type muscle activation to the quadriceps femoris. Depending on the availability of your exercise equipment, this plethora of alternative exercises can readily make up for the hypertrophy induced by leg extensions in your workout routine.
As the leg extension exercise utilizes what is referred to as an open kinetic chain wherein the distal point of the body is left free to move, the leg extension is classified as an upper leg-focused open kinetic chain movement.
This, by extension, means that the leg extension is an isolation exercise primarily targeting the quadriceps femoris. The quadriceps femoris is a group of four muscles with distal insertion or attachment points at the patella, and origin or proximal attachment points at the anterior point of the femur (thigh bone).
Knowing this, we can surmise that the quadriceps are the main muscles primarily responsible for drawing the leg towards the chest.
In layman’s terms, the leg extension exercise generates the most movement from the muscles in your outer-facing thigh, a distinction which should be immediately apparent if you are performing the exercise with the correct form.
The leg extension is most often performed seated with an adjustable roll of padded foam or rubber placed in the crook of the exerciser’s ankles, with the feet turned upwards in order to ensure that it does not roll off the legs.
The exerciser will then slowly raise their calves upwards while keeping themselves steadily in place on the seat, with the primary movement being focused on their lower legs. This is referred to as the concentric portion of the movement, and is when the primary contraction of the quadriceps femoris muscle group occurs.
Once the legs have been fully extended so as to nearly replicate the position of standing, the exerciser will slowly lower their legs once more, performing the eccentric portion of the exercise as the quadricep femoris muscle group begins to relax.
Much like its name, the quadricep femoris muscle group consists of four primary muscles that are placed in a “fan” around the femur bone, allowing the human to perform a nearly full range flexion or extension motion with their legs.
The outermost pair of these muscles are dubbed the Vastus Lateralis and the Rectus Femoris, of which are on the outer side of your thigh and the top of your lap.
While it is true that any sort of leg exercise involving the quadriceps will activate all four muscle groups, this activation is not often equal, and depending on your particular injury or exercise goals, you may wish to specifically perform exercises that share a larger focus on certain parts of the quadricep femoris muscle group.
The dumbbell sumo squat is a free weight exercise that not only targets the rectus femoris and vastus lateralis but also other muscle groups in the leg such as the calves and hamstrings. This means that, if you are otherwise unable or unwilling to target these muscle groups, the dumbbell sumo squat is an unsuitable replacement for leg extension alternatives.
The dumbbell sumo squat is performed by gripping a dumbbell between both of the exerciser’s upward facing palms. The exerciser will then set their feet slightly wider than shoulder-width apart with the heels planted firmly and their toes facing outwards.
Using their hips as the basis of the movement, the exerciser will lower themselves until their knees are at least parallel with their hips, all the while keeping their back as straight as possible and their chest facing upwards. This is vitally important, as improper form may cause injuries.
In much the same way that they have lowered themselves, the exerciser will then raise themselves once more, ensuring that their back is straight and their chest is facing upwards.
The barbell hip thrust also includes the hamstrings and gluteus maximus muscles in its movement chain and as such is an unsuitable replacement if you are unable or unwilling to activate these muscle groups.
The barbell hip thrust is performed by first laying one’s back against an elevated surface such as a bench or chair, with the buttocks facing towards the floor and the legs partially extended towards the ground. Weights such as barbells, dumbbells or even simple weight plates are placed in the lap of the exerciser, who will keep their back as straight as possible.
With the feet firmly planted, the exerciser will “thrust” their hips upwards, essentially creating a flat plane from their knees to their chest. Ideally, the hips must be at least parallel with the shoulders of the exerciser in order to best activate the vastus medialis muscle.
A far less intense exercise than the other two mentioned in this article, the unweighted leg raise also requires no equipment apart from a comfortable area to lie down. Keep in mind that this exercise will also activate the abdominal muscles, and as such is unsuitable for people with hernias or similar abdominal injuries.
In order to perform the unweighted leg raises, simply lay on the floor with your back flat and straight, preferably cushioned by a yoga or exercise mat. Tuck your arms at your sides with the palms facing upwards, and keep the base of the skull in contact with the ground as much as possible.
Slowly raise your legs upwards, ensuring that they are completely straight and the feet are pressed tightly together. Do not raise your back off the floor, as this will shift the focus of the exercise to different muscle groups.
Raise the legs as far as is comfortable for you, and hold this position for approximately two seconds, before lowering them back to the ground.
The benefit to this particular exercise, apart from its convenient nature, is that it is quite low impact and perfectly suitable for most healthy individuals of any age.
As this article has covered the two outer muscles that make up the quadricep femoris muscle group, this section will focus on the two remaining muscles that make up the inner portion of the thigh. These muscles are often ignored by gym-goers owing to their less visual nature; however, they are of no less importance and contribute greatly to the stability and function of the legs.
These two muscles are the vastus medialis, or the “tear-drop” muscle which possesses a distal insertion point at the inner portion of the knee, as well as the vastus intermedius, which lays beneath the rectus femoris and is one of the strongest muscles in the human body per square inch of tissue.
As always, exercises that target these muscles will also target the entirety of the quadricep femoris muscle group itself, and thus it is largely unavoidable that all four of the quadricep muscles will activate while performing these exercises.
The dumbbell split squat is performed by gripping dumbbells or weight plates of equal mass in both hands. Keep in mind that this exercise will activate the majority of muscle groups in your lower body, including smaller ones such as the calves and hip abductor or adductors.
Keeping your back straight and head facing forward, spread your legs with one placed forward and the other positioned behind the torso, essentially producing a “split” position.
Slowly lower your hips until the leg positioned behind you comes into contact with the ground via the knee. The leg facing forward should also bend at the knee, as if you were kneeling. All the while, ensure that your spine is kept completely straight and your body is evenly positioned so as to distribute the muscular activation in a balanced manner and to reduce the chance of injury.
Raise yourself in much the same manner that you lowered yourself. Alternate the position of your legs between sets or even between repetitions of the exercise.
This exercise requires an exercise ball or other exercise-safe object made of flexible material that can withstand being crushed between your legs.
Simply take a seat on a bench or chair and place the exercise ball between your thighs. Ensure that it is securely in place before attempting this exercise.
Squeeze the exercise ball by attempting to close your legs with the ball still present between your thighs. Hold this position for several seconds before releasing the ball.
As a very low impact exercise, exercise ball squeezes are excellent for patients undergoing physical therapy or members of the elderly population.
Barbell kneeling squats are as close a quadricep-only isolation exercise as possible to leg extensions, though this exercise will still activate certain muscles of the hip adductor muscle group.
Kneeling on a comfortable surface, raise a barbell to the shelf of your shoulders and trapezius muscles, located at the rear of your neck. Place your hands at an even and comfortable length along the barbell, ensuring that your grip is firm and that the barbell will not slip.
Straighten your hips in such a way that your knees, still in contact with the ground, are approximately parallel with your chest. The front of your torso and thighs should form a relatively flat plane, with the main distribution of weight being evenly placed throughout your back and legs. As always, keep your spine as straight as possible, including the position of your head and neck.
Lower yourself until your gluteus maximus muscles have made contact with your calves or heels, completing the eccentric portion of the exercise. Ensure that your knees remain in contact with the floor all throughout this exercise in order to prevent any injuries to your quadriceps.
1. Signorile, Joseph F.; Lew, Karen M.; Stoutenberg, Mark; Pluchino, Alessandra; Lewis, John E.; Gao, Jinrun (September 2014) Range of Motion and Leg Rotation Affect Electromyography Activation Levels of the Superficial Quadriceps Muscles During Leg Extension, Journal of Strength and Conditioning Research
2. Chaitow, Leon; DeLany, Judith (January 2011), Chaitow, Leon; DeLany, Judith (eds.), "Chapter 13 - The knee", Clinical Application of Neuromuscular Techniques, Volume 2 (Second Edition), Oxford: Churchill Livingstone