Did you know that an ACL injury not only affects your knee, but also creates changes in your brain?
In this article, I am going to tell you what actually changes in your brain after an ACL injury, explain how those changes might impact your function or sport performance, and show you how to incorporate training the brain into your ACL rehab program.
Do you need help with your ACL rehab? Check out our 1-on-1 consultation and coaching services!
Neuroplastic Changes After An ACL Injury
Let me start by explaining the neuroplastic changes that occur after an ACL injury.
Neuroplasticity is your brain’s ability to adapt and change. This happens as the result of new experiences, learning new things, or, in this case, injury.
If you’re sitting down right now, chances are that you don’t have to look at your knee to know that it is bent. That’s because there are receptors in the joint that send information to your brain about how your joint is positioned. This sensation of joint position is called proprioception.
If you decide to stand up and walk away, your brain will take in information about the environment around you, like if there are any obstacles in your way, and then create a plan to produce the necessary movements. Using visual input to plan and produce movement is done by the visual-motor system, and this all happens automatically without you having to think about it.
When the anterior cruciate ligament (ACL) is injured, the messages about proprioception become disrupted. As a result, the brain starts to rely more heavily on the visual system to tell it information about the knee’s positioning.
Since the brain is compensating for this impaired proprioception by increasing its reliance on vision, it loses some of its ability to scan the environment and look out for obstacles that might be in your way.
In addition to this, there is something called arthrogenic muscle inhibition that occurs after an ACL injury. In 2015, Lepley et al found that individuals who had undergone ACL Reconstruction 6 months prior “required higher stimulation in order to cause depolarization of the neurons in the primary motor cortex.” This just means that it requires more signals than normal from your brain to your quadriceps muscles for them to contract and initiate movement. In other words, it’s harder to make your quads work.
Your brain compensates for this by using the areas that usually respond to the environment and plan movement to help generate a quad contraction instead. You end up spending more brain power to perform simple movements which takes away from the brain’s ability to make last minute adjustments and move automatically.
A 2009 study by Kapreli et al found that ACL deficient patients had increased activity in the motor planning areas of the brain compared to healthy controls. Grooms et al in 2017 had similar findings in patients who had undergone ACL reconstruction 6 months to 2 years prior compared to healthy controls. Specifically, they found that there was increased activation in the contralateral primary motor cortex, ipsilateral lingual gyrus, and secondary somatosensory cortex. These findings highlight that there is a need for increased cortical drive in order to engage the quads, that there is an increased reliance on feedback from the visual system in order to coordinate appropriate limb positioning, and that there are increased processing demands in the brain in order to maintain motor control integrity.
Both the Kapreli and Grooms studies also found that those with ACL deficient or reconstructed knees had decreased activity in the sensorimotor areas of the brain which affects the ability to make rapid motor corrections.
All of this essentially means that there is less information coming from your knee to your brain. Your brain adapts by trying to get that information elsewhere – mostly from your visual system. The brain also starts using more of its processing power to generate muscle contractions around the knee and produce movement. It does this by hijacking some of the areas of the brain that are usually reserved for planning and coordinating movement.
How Rehab Perpetuates These Neuroplastic Changes
Not only do these neuroplastic changes occur as a result of the injury, but they are further perpetuated by the compensatory movement strategies used after an ACL injury, as well as certain aspects of the rehabilitation program itself.
For example, an exercise you might do very early after an ACL reconstruction is quad sets.
It might be tempting to stare at your knee and thigh while performing this exercise to make sure you’re contracting your quads. However, since your knee is now sending disrupted messages to your brain about its positioning, the brain is already relying too much on vision for this information. Staring at your knee and thigh during this exercise just perpetuates that reliance. It’s ok to look at your leg initially when you first begin this exercise, but you should eventually try to do it without looking.
Another example is doing exercises like squats or lunges in front of a mirror. It might be helpful at first, but eventually you have to take that mirror away so you do not become reliant on that visual input.
It is important to address these neuroplastic changes and “train the brain” during ACL rehab because functional and sporting tasks require automatic movements in response to the environment. You can’t be dependent on watching your knee while you’re trying to run, jump, or play your sport.
An athlete like a soccer player needs to be able to scan the environment, take in information about where they are in relation to the goal, their opponents, their teammates, and the ball, listen to their coach and teammates, and make quick movement decisions in response to all these things.
After an ACL injury, the parts of the brain normally dedicated to processing visual feedback from the environment are instead being used for feedback about knee joint position, and the areas of the brain that are meant to make rapid motor corrections, like having to cut away from a defender at the last second, now have decreased activity. This could have an array of negative consequences including poor performance and increased risk of yet another injury.
How To “Train The Brain”
So how do you actually “train the brain” in ACL rehab?
Grooms, one of the leading researchers in this field, and his colleagues in 2015 state that an ACL rehab program should aim to address the neuroplastic changes that occur with an ACL injury by implementing visual-motor training.
Visual-motor training refers to training the system that helps you scan the environment and produce movement in response. It can be done through dual-tasking, which is essentially performing two tasks at once.
The most important ways to perform dual-tasking are with either visual obstructions or environmental interactions.
- Visual obstructions can be created with the use of stroboscopic glasses which have lenses that flicker between clear and opaque to obstruct vision, eyes closed or blind-folded conditions, or through the use of augmented or virtual reality.
- You can include environmental interactions by performing a movement while having to look around you.
It sounds like a lot, but I am going to show you how these neuroplastic changes can be addressed, embedded within a holistic rehabilitation program, from the acute stage all the way through to return to sport.
Keep in mind that these are merely suggestions and this is not an exhaustive list of all the many ways you can “train the brain” in ACL rehab.
Early Stage Rehab
The top priorities right after ACL reconstruction are decreasing effusion, or swelling, and increasing range of motion while trying to decrease the rate of atrophy or muscle loss. Some of the most commonly performed exercises are quad sets, heel slides, and straight leg raises.
As I mentioned earlier, it’s tempting to want to look at your knee as you perform these exercises.
In order to decrease reliance on vision, close your eyes or at least look away from your leg. You can include visual-motor training through an environmental interaction by looking at a screen that flashes colors and performing the exercise when a specific color comes up.
You can test your brain even more by varying your exercises. For instance, every time the color green flashes on a screen, you have to do a straight leg raise, every time red flashes, you have to do a heel slide, and every time yellow flashes, you have to do a quad set.
You can get as creative as you want here. The number one priority is relying on your vision as little as possible for these basic exercises without sacrificing improvements in your range of motion or quad activation.
Mid Stage Rehab
In the mid stage of rehab, the primary goals are muscle hypertrophy, movement quality, and keeping a quiet knee, which means minimizing swelling and maintaining range of motion. Here are some common exercises performed in this phase of rehab and neurocognitive considerations for each:
Knee Extensions
Don’t look at your knee while performing. Instead, close your eyes, look at an external visual cue like a specific color or word being shown on flash cards or a screen to trigger the movement, or wear virtual reality goggles and perform the movement in response to a cue there like kicking a ball.
Squats
Movement quality is an important aspect of this stage of rehab. It can initially be helpful to watch yourself in a mirror when performing exercises like squats to ensure the movement is done with control. However, if you want to decrease reliance on the visual system, you should eventually try to take the mirror away.
If you still need help with the quality of your movement, there are other things you can try. For example, you can attach a laser pointer to your knee and try to keep it pointed straight ahead. If you don’t have laser pointers, you can still use this cue by imagining laser pointers coming out from your kneecaps.
You can also try to watch a video of someone else doing the movement and mimic it instead of watching yourself in a mirror.
Step-Ups / Step-Downs
You can introduce dual-tasking with an environmental interaction here by stepping up or down to catch an object being tossed to you.
Standing Balance
It can be fun to get creative during standing balance challenges. Aside from the typical shoes on, shoes off, and standing on unstable surface conditions typically done in rehab, you can perform dual-tasking by juggling or solving cognitive challenges like remembering sequences of numbers or words, completing math problems, or answering trivia questions.
If you have the equipment, you can use virtual reality goggles to watch an immersive sport video like skiing or surfing, or even riding a roller coaster, while trying to maintain standing balance.
A side note on balance exercises: try not to combine balance exercises with exercises being used for strength or hypertrophy. Being on more stable footing is better for higher force production which is needed when trying to gain muscle mass and strength.
Also, since regaining muscle mass is one of the primary goals here, you don’t have to incorporate all of these elements into every set, exercise, or training session. For example, you might incorporate these principles into 1-2 exercises per training session rather than overhauling your entire program at the expense of the other specific adaptations important to ACL rehab.
Sometimes your focus just needs to be on executing a movement to failure, or close to it.
Late Stage Rehab
In the late stage of rehab, the focus is pure strength and power. You can also begin to introduce plyometric and change of direction activities in this phase. This phase is really fun because you can get creative in the exercise prescription and there is a seemingly limitless way to incorporate training the brain. Here are a few examples:
Jumping Variations
You can add dual-tasking by jumping in response to a moving target, like jumping up to catch a ball or by having to react to a visual stimulus like a flashing light in order to perform a jump.
While I wouldn’t necessarily recommend performing many jumping variations blind-folded for safety reasons, your physical therapist might have other tools such as stroboscopic glasses to provide visual obstructions while jumping.
Change of Direction Tasks
When performing change of direction tasks, you typically begin with pre-planned, submaximal movements, progress into pre-planned maximal movements, then reactive sub-maximal movements, and finally into reactive maximal effort movements.
A partner chase game or game of “tag” is a great way to add a reactive component with dual-tasking because you have to watch and respond to your partner while moving.
If you have the equipment, there are some great virtual reality games that incorporate reactive movements and submaximal change of direction tasks. A few of my favorites are Rezzil Player, PowerBeats VR, Holopoint, and Eye of the Temple.
Common Mistakes
Common mistakes made when it comes to implementing these strategies are being overwhelmed and then not doing them at all as a result, forgetting the basics and doing exercises that look fancy at the detriment of creating true adaptations for the physical qualities needed after ACL injury, simply tacking on an extra 15 minutes at the end of the session to do it, and waiting until late stage rehab to start training the brain.
Summary
I know I covered a lot. The main things I hope you take away from this article are:
- That an ACL injury affects more than just the tissues in the knee. It creates neuroplastic changes that are a disruption to the sensory input coming from the knee to the brain which leads to an increased reliance on the visual system. There is also disrupted output from the brain to the injured limb which leads to more of the processing and motor planning areas of the brain being needed to produce and control movement which creates even more of a need for visual input to help with the processing and planning of movement.
- There are specific ways that you can “train the brain” during ACL rehab to address these neuroplastic changes. The most important way to train the brain is through dual-tasking to address the changes in the visual-motor system after an ACL injury.
- Finally, these interventions to “train the brain” do not have to be overly fancy or their own separate rehab sessions. They can be weaved into a holistic ACL rehab program.
Do you need help with your ACL rehab? Check out our 1-on-1 consultation and coaching services!
Want to learn more? Check out some of our other similar blogs:
ACL Rehab (Start To Finish), ACL Plyometric Exercises (4 Stages), Leg Extensions After ACL Reconstruction
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