Electrical Stimulation After ACLR

Shockingly Good? Or Just a Bit of Buzz?

If you're on this ACL journey, whether as a patient staring down a stubbornly sleepy quad or a Physio trying to coax said quad back to life, you know the struggle is real.

That big, beautiful quadriceps muscle on the operated side often decides to take an unscheduled, extended vacation post-ACLR.

This isn't just a fleeting issue; as Arhos et al. (2024) highlight, quadriceps inhibition and weakness are ubiquitous and persist from early after injury right through to when athletes are trying to get back to sport.

We call this rather rude phenomenon Arthrogenic Muscle Inhibition (AMI), and frankly, it’s a pain in the, well, knee!

This quad shutdown isn't just a party trick; it's a major hurdle.

As Moiroux-Sahraoui et al. (2024) point out, persistent weakness here can mess with your walking, lead to muscle wasting (atrophy), contribute to ongoing pain, and even increase the risk of nasty things like re-injury or early osteoarthritis down the track (Arhos et al., 2024).

It’s a key reason why getting back to sport can feel like climbing Everest in thongs (or flip-flops for my American friends).

So, what’s in our physio toolkit to give that quad a friendly (or not-so-friendly) wakeup call?

Enter Neuromuscular Electrical Stimulation, or NMES…

NMES is essentially using electrical currents to get the muscle contracting when the brain-to-muscle communication line is a bit staticky.

Arhos et al. (2024) explain that NMES combats this muscle inhibition by facilitating the recruitment of muscle that might be held back by pain or swelling, essentially overcoming impaired activation by boosting motor unit recruitment and how fast those motor units fire. It's like a direct dial to the muscle fibres, bypassing some of that pesky inhibition.

But the million-dollar question is: does it actually work in the complex world of ACL rehab? Is it worth the zap? Let’s take a look at what some recent research has to say.

The Shocking Truth: What the Science Says About NMES

A big systematic review and meta-analysis by Li et al. (2025) recently crunched the numbers from a host of studies, and the findings for quad strength were pretty encouraging.

They found that adding NMES to standard rehab resulted in significantly better quadriceps strength compared to standard rehab alone. We’re not talking tiny differences here; some individual studies they reviewed showed NMES groups achieving an extra 10-25 percentage points.

And this isn't a new fad.

The evidence for NMES is strong – so strong, in fact, that the 2017 clinical practice guidelines gave NMES an "A" grade recommendation (Arhos et al., 2024).

Read the full text Clinical Practice Guidelines here

Timing of NMES seems to be key though.

The review by Li et al. (2025) suggested that starting NMES early (within the first week post-op) led to even bigger improvements in quad strength compared to starting it later.

This idea of "early intervention" is backed up by other research.

For instance, a cracker of a study by Toth et al. (2020) looked at using NMES right after injury and continuing until 3 weeks after surgery. They found that this early NMES significantly reduced the amount of muscle fibre atrophy (shrinkage) at the 3-week post-op mark. The NMES group lost about half as much muscle fibre size compared to the sham group, especially in those powerful fast-twitch fibres! They also saw some positive effects on how well individual muscle fibres could contract. While these early cellular benefits didn't automatically translate to stronger whole muscles at 6 months in their study (possibly because the NMES was stopped quite early), it highlights that NMES might be working its magic right down at the microscopic level from the get-go.

Similarly, Labanca et al. (2022) investigated an early NMES program (day 15 to day 60 post-op) superimposed on functional movements. Their NMES+ group showed significantly greater knee extensor and flexor strength, and better limb symmetry in strength, not just in the short term but also at a long-term follow-up of over a year!

But it’s not just about how big or strong the muscle is. It’s also how well it works.

Jo and Kim (2025) explored this by looking at a 6-week NMES program. They found it led to significant improvements not just in force production (MVIC) but also in force steadiness (meaning better control) and even positive changes in motor unit characteristics (like increased motor unit action potential and numbers). Using ultrasound, they also saw improvements in muscle quality, with muscle thickness increasing and echo intensity (an indicator of muscle health) improving. They noted that while some benefits appeared by 3 weeks, the full 6-week stint was generally needed for more substantial results.

Does NMES Help Us Move Better Though?

Okay, so strength is improving, maybe muscle quality too.

But does this translate into better movement patterns, like during a landing?

This is crucial for getting back to dynamic sports.

Lepley et al. (2015) looked into this and found that a combined NMES and eccentric exercise program was the most effective of the interventions they tested for improving knee extension moment limb symmetry during a single-leg hop. While quad strength symmetry was related to better biomechanical symmetry, it didn't explain the whole picture, suggesting NMES might offer benefits beyond just raw strength, perhaps in neuromuscular control or motor learning (Lepley et al., 2015).

What About Overall Function?

It's a bit more complex.

When Li et al. (2025) looked at patient-reported functional scores like the Lysholm knee score, the overall difference between NMES and control groups wasn't statistically significant across the board.

However, Labanca et al. (2022) did report that their early NMES+ group achieved significantly better limb symmetry during functional tasks like sit-to-stand, stand-to-sit, and even countermovement jumps at long-term follow-up.

This might mean that while NMES is a powerhouse for waking up the muscle and building a strength foundation (which is absolutely critical!), how this translates to overall functional scores (which can be influenced by pain, swelling, confidence etc.) might vary or take more time to become apparent. Or, as Moiroux-Sahraoui et al. (2024) suggest, tackling AMI might require a multifaceted approach, where NMES is one valuable tool alongside others targeting the muscle, brain, and peripheral nerves.

If NMES is So Good, Why Isn't Everyone Using It (Properly)?

This is a really important point raised by Arhos et al. (2024).

Despite the strong evidence, NMES isn't always used, or used effectively.

They point out that in a recent survey, only about half of therapists were aware of that "A" grade Clinical Practice Guidelines rating, and just over half used NMES for post-ACL rehab. And even then, it's unknown how many were dosing it therapeutically!

So, why the gap? Arhos et al. (2024) suggest a few reasons:

• It might not be included in standard post-op protocols.

• There can be a lack of knowledge on how to dose it correctly.

• Time pressures in the clinic – setting up another modality when hands-on time is precious.

And here’s a big one: historical under-dosing.

Arhos et al. (2024) highlight that some older studies didn’t use NMES at a high enough intensity (sometimes not even reaching 50% of the patient’s maximum voluntary isometric contraction or MVIC), which likely "washed out" the true benefits and sowed some confusion. Some studies even used machines that simply couldn't deliver enough juice! This underscores that to get the results, the dose matters – a lot! Foundational studies showed that high-intensity NMES was necessary to recover quad strength, outperforming low-intensity NMES and sometimes even high-level volitional exercise alone in the early stages (Arhos et al., 2024).

Getting the NMES Dose Right: The Nitty-Gritty

So, how do we make sure we're using NMES to its full potential? Arhos et al. (2024) offer some excellent clinical pearls: