In this blog, I show you how to set up, perform, and program leg extensions for strength, hypertrophy, and rehab purposes while discussing the latest research. Trust me, there’s more to leg extensions than you think!
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Quadriceps Anatomy & Function
First, a quick review of anatomy.
The quadriceps, or quads, consist of 4 muscles – the vastus medialis on the inside of the thigh (green), the vastus lateralis on the outside of the thigh (blue), the vastus intermedius deeper in the middle of the thigh (not visible), and the rectus femoris that sits over the top (red). All four muscles insert on the tibial tuberosity via the patellar tendon (yellow) and act to extend, or straighten, the knee.
The three vasti muscles originate from the thigh, whereas the rectus femoris originates up at the hip. Therefore, the rectus femoris also flexes the hip.
Leg Extensions Are Necessary For Strength & Hypertrophy
Most people are aware that if you want to increase the strength and size of your quads, you should incorporate exercises like squats, split squats, and the leg press because they involve knee extension, which is the primary action of the quads.
However, research by Ema et al in 2016 and Vigotsky and Bryanton in 2016 demonstrate that the rectus femoris provides little contribution to compound movements that require simultaneous knee and hip extension. For example, a paper by Kubo et al in 2019 found no growth of the rectus femoris in untrained lifters after 10 weeks of squat training.
On the other hand, studies by Maeo et al in 2018, Zabaleta-Korta et al in 2021, and Burke et al in 2024 have shown that seated leg extensions cause preferential hypertrophy of the rectus femoris.
Therefore, maximizing quad strength and muscle growth requires multi-joint exercises like squats in which the hips and knees are extending, as well as single-joint exercises like seated leg extensions in which only the knees are extending.
Leg Extensions Are Also Necessary for Rehab
In the presence of pain or swelling, such as after an injury or surgery, the body becomes good at compensating.
For instance, Sigward et al in 2018 found that 3 months after ACL reconstruction, individuals performed interlimb compensations during a squat. This means that if they had surgery on their right side, they loaded their left side more, which is often associated with an observable weight shift to that left side.
However, the participants also demonstrated intralimb compensations. This means that in addition to favoring their non-surgical leg, they offloaded their affected knee by working harder at the ankle and hip on their surgical side.
5 months after surgery, the participants no longer demonstrated interlimb compensations, but they continued to have intralimb compensations. So, what the researchers found was that even though the squats appeared symmetrical and normal, the individuals continued to redistribute the load from the surgical knee to the hip and ankle on that side.
And this information isn’t just relevant to squatting. It shows up in walking, hopping, and running.
Our bodies are naturally going to take the path of least resistance. If you have pain, swelling, or significant weakness due to an injury or surgery, you’ll find a way to work around those issues whether it’s a conscious decision or not. This can be true of other knee diagnoses, such as patellofemoral pain and patellar tendinopathy, as well conditions related to the hip or ankle in which the entire limb continues to be unintentionally offloaded.
Now, I’m not suggesting that leg extensions replace squats or other compound exercises. This is not an either/or scenario. However, leg extensions are beneficial because they completely isolate the quads, are nearly impossible to cheat, and can easily be modified or scaled to the needs of the individual.
I’ll discuss how to perform and program leg extensions specifically for rehab purposes toward the end of this blog.
How To Set Up Leg Extensions
When it comes to setting up leg extensions, there are several considerations.
The first is the position of the backrest. A recent study by Larsen et al assessed how the angle of the hip, whether being in a more flexed or extended position, influences hypertrophy. The researchers found “that rectus femoris muscle hypertrophy was greater with 40° [of] hip flexion compared to 90° [of] hip flexion with no differences between legs for vastus lateralis hypertrophy.”
They hypothesized that the greater hypertrophy seen in the rectus femoris at 40 degrees of hip flexion was due to training it in a more lengthened position.
On the other hand, there was no significant difference in the vastus lateralis because changing the angle of the hip has no influence on the length of any of the vasti muscles.
You don’t necessarily have to take this finding to the extreme. Try moving the seat back and leaning back instead of leaning forward.
The next consideration is your knee flexion angle. To emphasize the stretched position of the quads, adjust the machine so your knees are bent as much as possible. Some machines may limit you to only about 90 degrees of knee flexion, so if you want to increase that, you can place a foam pad, yoga blocks, or a folded up yoga mat between your shins and the padding of the machine.
The third consideration is the position of the pad. The pad should be on the lowest portion of your shins, just above your ankles.
Lastly, your feet should be facing forward. You don’t need to rotate your legs in either direction.
How To Perform Leg Extensions
When it comes to setting up leg extensions, there are several considerations.
To perform leg extensions, lean back, pull yourself down so your butt isn’t lifting off the seat, and use a controlled tempo. The weight stack shouldn’t be slamming down with each repetition.
In fact, I typically use a weight that’s too heavy for me to completely lock out my knees as a way of training the quads harder in a more lengthened position.
Most people will perform sets of 10-20 repetitions, myself included. However, there’s no reason you can’t perform more or less repetitions as long as you’re pushing yourself to failure, or close to it.
If you’re going to perform them one leg at a time, my preference is to put the opposite foot on the seat, but you can choose the strategy that works best for you.
How To Perform Leg Extensions At Home
For people training at home without a leg extension machine, avoid performing banded leg extensions throughout the full range of motion.
The issue is that the resistance of the band is greatest when the knee is completely straight and almost non-existent when the knee is bent.
This isn’t inherently bad, but you actually want the resistance to be greatest when the knee is bent. You also ideally want the band to remain fairly perpendicular to your shin.
Instead, set up a long, heavy resistance band in such a way that you’re unable to fully straighten your knee due to the high tension and perform partial repetitions. Research by Pedrosa et al in 2022 demonstrates that performing partial repetitions in this range of motion is superior for hypertrophy compared to the alternative, especially if you consider the other factors I just mentioned
If needed, put a towel in front of your shin for comfort and a pad under your distal thigh for better positioning.
Keep in mind that you may need to perform more than 20 repetitions to approach failure. For this reason, myo-reps can be a good choice here. For example, you can perform 1 set of 15-25 reps to failure, rest 10-15 seconds, perform 5 repetitions, and repeat this cycle of short rest and 5 repetitions for another 2-3 sets.
If the long, heavy resistance band is too difficult to set up, you can just perform isometric contractions using a belt, band, or some other object with minimal give to it. A systematic review by Oranchuk et al in 2019 found that “Isometric training at longer muscle lengths produced greater muscular hypertrophy when compared to equal volumes of shorter muscle length training.” The same systematic review also found that more volume and longer holds lead to more hypertrophy. Therefore, you can try to accumulate 30-60 seconds of total work for each set.
All of these options are done unilaterally and, if desired, can be performed flat on your back to put your hips in a more extended position.
Leg Extension Alternatives
If you’re looking for alternatives to leg extensions, consider exercises that primarily involve knee extension, such as reverse nordics, sissy squats, and rear foot elevated split squats that focus on putting your weight through the back leg instead of the front leg.
There are plenty of other exercises that emphasize the quads in general, like hack squats, heel elevated squats, forward step downs, and split squats with purposeful forward knee travel, but leg extensions are unique and advantageous because of their simplicity, their ability to be easily progressed, and their ability to isolate the quads and target the rectus femoris.
How To Program Leg Extensions For Strength & Hypertrophy
Adding leg extensions into your program can be pretty straightforward. If you train your legs 2 days per week, your routine might look something like this:
- Monday:
- 3 sets of hack squats
- 3 sets of dumbbell RDLs
- 3 sets of single leg seated leg extensions
- 3 sets of single leg seated hamstring curls
- 3 sets of machine calf raises
- Thursday:
- 3 sets of rear foot elevated split squats
- 3 sets of prone hamstring curls
- 3 sets of seated leg extensions
- 3 sets of hip extension on the roman chair
- 3 sets of single leg calf raises
Obviously there are unlimited possibilities. How often you train, how many sets you do per week, and the number of exercises you choose to perform per session will depend on your training experience, goals, and other factors. You might choose to do more sets than this example, incorporate the seated hip abduction and adduction machines, modify the training frequency, or swap out the leg extensions one day for reverse nordics instead. It’s all fair game.
How To Perform & Program Leg Extensions For Rehab
Performing and programming leg extensions for rehab doesn’t necessarily have to look any different than anything I’ve discussed up to this point. However, there may be times when modifications need to be made. I’ll provide examples for patellofemoral pain, patellar tendinopathy, and ACL reconstructions, but this information can be applied to most issues.
When it comes to patellofemoral pain, leg extensions are completely safe and cause no more stress on your knees than squats, especially when considering relative loads. If the lockout is uncomfortable, try using a partial range of motion. You can also use less weight and do more reps or try the isometrics I mentioned earlier (with a machine or band). Blood Flow Restriction (BFR) training is another possibility.
With regard to patellar tendinopathy, leg extension isometrics are beneficial for inducing positive tendon adaptations. Here’s one example of how seated leg extensions are applied in research:
- Bend your knee to roughly 60 degrees
- If you’re using a machine, make sure it’s too heavy for you to move
- Push at your maximum tolerable effort for 3 seconds, relax for 3 seconds, and repeat for 4 total repetitions
- Rest 1-2 minutes
- Repeat 4 more times for 5 sets total
- Perform this 3 times per week
Another example is doing 3-5 sets of 30-45 second holds with a 2 minute rest between sets. This can be done as a warm-up prior to workouts or as an independent stimulus, 1-2 times per day.
Three things to note here about rehab:
- Always perform leg extensions on your unaffected side first to get a feel for the movement.
- Ramp up and ramp down your effort the first few times you attempt isometrics, so you don’t accidentally get a spike in symptoms.
- Aim for the exercise to be challenging but tolerable. Adjust the weight, range of motion, etc. as needed.
And hopefully this goes without saying, but you should always get clearance from your physical therapist or medical doctor before initiating a new exercise after an injury or surgery, especially if you have concerns about the safety of the exercise.
Looking for rehab or performance programs? Check out our store here!
Want to learn more? Check out some of our other similar blogs:
How To Grow Your Quads, ACL Rehab, How To Perform Nordic Hamstring Curls
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