Leg Extensions After ACL Reconstruction

Marc Surdyka

April 9, 2023

Have you had an ACL Reconstruction?

In this blog, I explain why you SHOULD be doing leg extensions immediately after surgery, why leg extensions are safe despite popular belief, and provide you with step-by-step instructions on how to perform and program them.

Looking to improve your strength, range of motion, and power to enhance your function and performance? Check out our Knee Resilience program!

Why You Should Be Doing Leg Extensions After ACL Reconstruction

Let’s start with 2 reasons why you should be doing leg extensions after an ACL Reconstruction:

Long-term functional outcomes aren’t great. A systematic review by Ardern et al in 2014 found that only 55% of individuals return to competitive sport following surgery.
Reinjury is common. A systematic review by Wiggins et al in 2016 discovered that 1 in 4 athletes who are younger than 25 and return to high-risk sport will go on to have a second ACL injury.

Weakness of the quadriceps, the only muscles responsible for performing leg extensions, is one of the largest contributing factors to worse outcomes.

Research by Grindem et al in 2016 found that “quadriceps strength deficit prior to return to level I sport [sports involving jumping, pivoting, and cutting] was a significant predictor of a knee reinjury, with 3% reduced reinjury rate for every one percentage point increase in strength symmetry.”

A different study by Grindem et al in 2014 reported that even 2 years after surgery, ⅓ of people continue to have asymmetries in quad strength between their surgical and non-surgical legs.

It’s often assumed that squats and similar exercises are sufficient for maintaining and improving quad strength and muscle mass after surgery, but they actually allow for compensatory strategies to unknowingly offload the quads.

Sigward et al in 2018 found that 3 months after surgery, individuals will perform interlimb compensations during a squat. This means that if they had an ACL reconstruction on their right side, they load their left side more. And this might be 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 would offload 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.

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 knee pain or significant weakness of your quads due to an injury or surgery, you’ll find a way to work around those issues whether it’s a conscious decision or not.

Now knowing this information you might think you can avoid this problem by training your quads really hard starting 3 or 5 months after surgery, but it’s extremely difficult to make up for that lost time.

Or you might think you can overcome this problem early on by elevating your heels and using a mirror when you squat, but there are still going to be limitations in what you can accomplish. Leg extensions are the only exercise that fully isolate the quads and make it impossible to compensate.

Why Leg Extensions Are Safe After ACL Reconstruction

Now let me explain why leg extensions are safe after an ACL reconstruction.

I have never seen or heard of anyone tearing their ACL during a leg extension, and I couldn’t find a single example on the internet. However, as I mentioned earlier, there are a lot of examples of people re-tearing their ACL related to weakness of their quads.

More importantly though, a systematic review of randomized controlled trials by Perriman et al in 2018 aimed to “determine whether OKC quadriceps exercises [leg extensions] result in differences in anterior laxity, when compared to CKC [weight bearing exercises], at any time point following ACL reconstruction” and found no differences between the groups.

2 well-known ACL researchers, Brian Noehren and Lynn Snyder-Mackler, wrote an article in 2020 titled “Who’s Afraid of the Big Bad Wolf?” In it, they write that leg extensions are “(1) safe, (2) critical to restoring quadriceps strength, and (3) key for assessing readiness to return to sport.” They also state: “We encourage clinicians to fearlessly incorporate open-chain exercises into their rehabilitation programs.”

If you are still worried or skeptical about implementing leg extensions safely after an ACL reconstruction, I’m going to ease your concerns in the next section.

How To Implement

Apart from choosing not to do leg extensions at all, which I don’t recommend, there are 2 primary options:

Performing leg extensions through the full range of motion immediately after surgery since there’s no data to suggest they’re harmful. You also have to understand that the exercise, just like any other exercise or activity after surgery, is going to be self-limiting. You’re not going to sit on the leg extension machine day 1 and max out the weights. You’ll be limited by pain, weakness, and probably a bit of hesitation. Trying to perform 20 slow and controlled repetitions, with what would otherwise be considered a paperweight, is going to be challenging enough.
Option 2 involves doing static holds, also known as isometrics, between 60 and 90 degrees of knee flexion for the first 4 weeks after surgery, normal repetitions in a shortened range of motion between 45 and 90 degrees during weeks 4 through 12, and then the full range of motion after 12 weeks. Or some other variation of this protocol. I’ll explain why.

The more you straighten your knee during a leg extension, the more strain you place on the ACL. This is normal. However, I completely understand if you’re concerned based on what you’ve previously read, watched, or heard. That’s why I’m trying to present you with options.

Beynnon et al in 1995 found that isometric leg extensions between 60 and 90 degrees of knee flexion place zero strain on the ACL.

Other research has tested and suggested performing a shortened range of motion within the first few months due to the fact that there’s less strain.

The reason that I’m fine with either option is because you can argue that option 2 is just as effective, if not more effective, than option 1 based on systematic reviews by Oranchuk et al in 2019 and Wolf et al in 2022.

Oranchuk et al found that isometrics at longer muscle lengths lead to greater hypertrophy and improvements in strength throughout the full range of motion.

Wolf et al found “that performing partial range of motion resistance training at long muscle lengths results in greater muscle hypertrophy than both partial range of motion resistance training at short muscle lengths and full range of motion resistance training.”

In the case of leg extensions, long muscle lengths refer to the bottom portion of the exercise in which your knee is most bent.

This position can also be advantageous for any patellar tendinopathy or patellofemoral pain issues that may arise throughout the rehab process.

Therefore, I’m not even opposed to someone doing isometrics or shortened range of motion repetitions between 60 and 90 degrees of knee flexion for the majority of rehab.

Practical Application

There are 4 ways to apply this information:

1. The first is using a leg extension machine. I’m using what’s called a plate-loaded machine because that’s what I have available to me for filming. I’d generally recommend a pin-loaded machine because the resistance is constant throughout the range of motion. If you’re performing isometrics, you could max out the resistance of the machine so you’re unable to move it.

2. The second option is using a long resistance band and setting it up in such a way that you’re unable to fully straighten your knee due to the high tension. This variation is likely less than ideal early on because it can be tricky to get into the position.

3. The third option is using a belt, band, or some other object with minimal give to it. This is preferable to option 2 in the early stages because it’s typically easier to set up.

4. The fourth and final option is using an exercise ball that is placed against a wall.

If you’re performing isometrics, you can try to accumulate 30-60 seconds of work for each set. For example, you can do 3-5 sets of 30-45 second holds, 3-5 sets of 6 repetitions of 10 second holds, or 3-5 sets of 10 repetitions of 5 second holds. It’s whatever you’re comfortable doing.

These are going to be graded repetitions. This means that you’ll ramp up your effort based on your comfort. For instance, you’re not going to kick all out in the first 5 seconds of a 45 second hold. You’ll build up that intensity slowly based on what’s tolerable for you.

If you’re performing repetitions within a shortened range of motion, you can set the goal of 15-25 slow and controlled repetitions.

Whether you’re doing isometrics or a shortened range of motion after surgery, one of the main goals is simply for you to improve your confidence and tolerance to active knee extension. Yes, you want to maintain your strength and muscle mass. Yes, leg extensions can help reduce swelling and muscle inhibition. But just focus on the process of being comfortable performing leg extensions and gradually doing more over time.

Based on that understanding, you can likely do these exercises daily at first depending on your pain and soreness. As your function improves and you place more of an emphasis on intensity, effort, and the speed of your effort with the isometrics, you’ll want to follow more traditional guidelines of resting 1-3 days between sessions.

The last thing I want to mention is that you should definitely be doing leg extensions on both legs. Your rest times can be the time it takes to alternate back and forth between legs.

Make sure that you’re pushing yourself on your non-surgical side. You shouldn’t be using the same weight or effort. It’s of the utmost importance that you try to maintain and improve the strength of your uninvolved leg. Let your surgical side catch up instead of letting your non-surgical side fall back.

Summary

In summary, leg extensions are safe after an ACL reconstruction. They should be used soon after surgery to improve short and long-term function and reduce your risk of reinjury upon returning to sport.

If you’re worried about the strain on your ACL, repetitions or isometrics performed between 60 and 90 degrees of knee flexion place zero strain on the ACL while still providing beneficial adaptations related to strength and hypertrophy.

Leg extensions can also be performed prior to surgery or as part of the rehab for non-surgical management.

What if your doctor or physical therapist is adamantly opposed to leg extensions? Well, hopefully you can have an open discussion with them that includes this blog and the research presented within it. If someone is going to say that leg extensions are dangerous, they should have the research to support that statement.

Don’t forget to check out our Knee Resilience Program!