Leg extensions are an effective way to strengthen the quadriceps muscles. Here are eight reasons to use this exercise in your leg day routine, as well tips for how to do it like a pro, and more.
The leg extension is a classic lower body exercise when it comes to leg machines.
Typically paired with a leg curl machine, the leg extension machine is popular with lifters of all ability for a variety of reasons, not the least of which is its excellent ability to target the four muscles that make up the quadriceps.
In this guide to the leg extension, we are going to look at:
- ALL the benefits of leg extensions
- The primary muscles worked during the exercise
- How to do it like a pro
Let’s jump right in.
Benefits of Leg Extensions
First, let’s take a more comprehensive look at the full range of benefits to the mighty leg extension.
Quad development 9000
The leg extension is almost exclusively an exercise for developing the four muscles that make up the quadriceps.
- Vastus medialis
- Vastus lateralis
- Vastus intermedius
- Rectus femoris
The rectus femoris is the most commonly injured quad muscle in athletic activity  and is the only one that crosses over into the hip.
Excellent for unilateral training
The leg extension provides an excellent opportunity to train unilaterally (one side of your body or one limb at a time).
Training unilaterally is a great way to help train your way out of muscle imbalances, recruit more muscle, and get a better sense of just how much we lean on our dominant side when doing bilateral lifts.
Lifters of all abilities, from beginners to pros, often lose a sense of how much they use their dominant side to compensate when lifting.
One of the main reasons people get injured in the gym is the compensation of some kind that alters technique or places undue strain on muscles that aren’t trained for it.
This is why I am such a huge fan of single leg exercises, whether they are split squats, lunges, or in this case, single leg extensions.
While the big bilateral movements like barbell back squats will also rule the roost when it comes to total power output, single leg variations keep you honest and keep your body from subconsciously “cheating” reps to compensate for the weaker links in the chain.
As a competitive swimmer, our strength coach emphasized the importance of this particular exercise as it related to our capacity to kick with more power in the water.
My sport is far from alone in this regard. Whether you are a cycist, runner, soccer player, or engaged in any sport that is quad-heavy, leg extensions are a go-to exercise for developing more power and stamina.
While there are plenty of leg exercises that athletes should pay more attention to—multijointed movements like front squats, jump squats, and even box squats—the leg extension can play a role for the developing athlete.
Excellent for beginners
Squats will always reign supreme, both in terms of functionality and strength development, particularly when it comes to developing quad strength.
But there are plenty of instances where squats are not the best option.
For people coming off an injury, for example, or those of you who aren’t ready for the more technical aspects of squatting correctly (not as simple as it looks—you’d be surprised how many lifters botch this “basic” exercise).
The learning curve on leg extension is straightforward and easy to work through. The limited range of motion and fixed path of the resistance means it’s, well, less likely that we will screw up and hurt ourselves on it!
Building muscle awareness
Experienced lifters who want to be better in tune with the eccentric and concentric phases of a quad-dominated lift should ABSOLUTELY do leg extensions.
Because your quads are right in front of you (as opposed to below you as with squats), you can really see the musculature flex and contract as you raise the padded bar up and down.
There is something about the visual feedback that comes with seeing your muscles flex in real-time under resistance to give you a better sense of how your leg muscles are contracting to counter resistance. (Can you tell I like nerding out about this stuff?)
Bodybuilders in particular will appreciate this aspect of the exercise—giving you full control and awareness of how your muscles are reacting to load.
Leg extensions are great for rehabbing
The closed nature of the lift and total isolation on the quadriceps means people with shaky knees, whether from a recent injury or extended periods of inactivity, can exercise the quads without risking straining the tendons and ligaments around the knee.
The leg press is another good example of an exercise that allows you to place individualized and controlled load on the knee.
Obviously, if you are working towards strengthening the knee, you will want to eventually progress to exercises that steadily increase in load.
A sample progression could look like this: leg extensions -> leg press -> box squats -> barbell back squats.
Leg extensions are a good exercise for those of us who have wobbly knees as it reduces load vertically on the knee and allows you to direct your energy on the contraction of the quadricep.
The VMO, the teardrop muscle that is right next to the knee, is part of the quadriceps and functions primarily as a knee stabilizer.
Great exercise for “finishers”
Because you are sitting down when doing this exercise, it’s a great choice for a “finisher” exercise where the goal is maximum reps until failure.
Exercises like barbell squats aren’t always a great choice for finishers—nobody wants to fail and ditch a loaded barbell, after all-with the leg extension providing a safe alternative for burning out your quads at the end of a big leg day workout.
Once you’ve done your big lifts for the day, go for maximum pump and burn by doing a high-rep set with moderate weight to failure.
Leg extensions are safer than many free weight exercises
At the end of the day, and this goes primarily for beginners and even some intermediate lifters, lifting weight confidently and safely is the priority.
The leg extension machine has you sitting down, reducing the concern one might have about lifting with proper technique and posture.
Because you are sitting and in a controlled movement, there is less that can go wrong.
Tips for How to Do the Leg Extension Like a Pro
While the leg extension is a relatively simple exercise, there are some important things to keep in mind when doing it so that you can maximize muscular growth and reduce injury.
Here are some tips for doing the leg extension like a certified champion:
Maximize time under tension.
Once you’ve descended the foot roller pad back to the bottom position, avoid the urge to “drop”.
Instead, do a controlled stop, pause, and then go back up. More time under tension results in more muscle activation.
Lower with control.
To piggy-back the previous point, don’t lose out on the strength and power gains by “dropping” your feet after you’ve reached the top of the movement.
Remember: tension is king!
Use it for hypertrophy.
This isn’t really an exercise designed for maximum power and strength, but rather building muscle.
For power and strength lifters, leave the leg extension towards the end of the workout for “finisher” sets.
For lifters and gymgoers looking for hypertrophy, feel free to put it closer to the front of your workout so that you are more fresh.
At the end of the day, most isolation exercises are best-suited for hypertrophy, with the big compound exercises like squats and deads better suited to max power.
When sliding into the leg extension machine, there are a few adjustments you will likely have to make.
The seat pad may need to be pushed back, and the workarm that has a removable pin and adjusts the foot roller, should be moved so that the pad lands diagonally from the bottom of your heel. It should not be on the top of your foot nor should it be halfway up your shins.
Avoid hyperextending the knees
One of the scarier “please don’t” things lifters do with this exercise is accelerate the foot pad skywards at bottleneck speed into a hyperextended knee lockout. For lifters with Gumby legs, avoid the urge to go past lockout with this exercise.
The Bottom Line
The leg extension is a familiar machine to most people who have been to the gym. The movement is simple, and the recruitment of the quads is effective.
How you choose to use it in your training regimen ultimately comes down to what you are hoping to achieve in the gym today.
Whether you are looking to strengthen the knee, build more muscular quads, or you want to get that “burn” at the end of a big lifting day, the leg extension is a great choice.