An anterior cruciate ligament (ACL) tear is not only a knee injury, but also a disruption to the nervous system. Some of the neuroplastic changes we see in association with ACL injuries are errors of estimation, increased reliance on visual feedback, and decreased motor cortex excitability. There are some common compensations that we tend to see in athletes after an ACL reconstruction (ACLR) such as decreased knee flexion during deceleration and change of direction tasks. These negative movement compensations and neuroplastic changes may even be further embedded by our current rehabilitation practices.
What many of us fail to realize is that one of our main roles as rehab professionals is that of a teacher. The athlete needs to learn how to perform certain tasks again without the compensations often seen after an ACLR that may put them at increased risk of reinjury. When an athlete goes back to their sport, they need to be able to interact with the environment, multi-task, and perform the sport with automaticity. It’s no good to the athlete if they’re able to perform a perfect squat in front of a mirror in the clinic if they cannot efficiently land from a jump on the field or court. Rather than being satisfied with short term technique success, we should be seeking true long-term motor learning. In order to effectively achieve this, we need to be cognizant of ways that we can utilize our cues, feedback, and the environment in order to drive implicit learning versus explicit learning.
Before we delve in to how we can help drive the motor learning process, we should first discuss why we need to strive for implicit learning over explicit learning.
Implicit learning is when a skill is learned in such a way that you cannot be consciously aware of how you are performing it. For example, when you learn to ride a bicycle, you don’t go to a special bicycle riding coach, clinic, or camp. You do not have someone program a specific progression for you with instructions along the way such as, “push your right foot down into the pedal as you bring your left hip up into flexion”. Instead, you sit on the seat, hold onto the handlebar, and someone pushes you along until you catch on. Sure, you may fall a few times, but the entire process is reflective of implicit learning. A huge benefit of implicit learning is that it is long-lasting skill acquisition, and not a transient success. You could go years without riding a bicycle, and yet as soon as you get on one again, you automatically know what to do.
When an athlete has a particularly stellar performance, they often report feeling as though they were “in the zone”. This means that they were able to tune out distractions, obliterate pressure, multi-task, and perform under fatigue. It is quite impossible to do these things when you are constantly in your own head trying to think about how you should be performing each and every movement. No athlete is going to perform well if they are thinking about how much knee flexion they have after their follow through from a shot on goal. And yet, this is exactly what we are teaching them in their rehabilitation programs. In fact, Rich Masters has done some great work in the field of implicit learning showing that having too much conscious control of movement disrupts automaticity, and those who place too much conscious control in their movements end up performing worse under pressure.
We’ve likely all seen an athlete after an ACLR go to perform a squat and shift off their surgical side onto the uninvolved leg. A common cue given in this scenario is to place a mirror in front of the patient so that they can see when they shift and hopefully correct it. While this cue may be helpful initially, it may also be driving that increased dependency on visual cues for proprioceptive information. Perhaps taking the mirror away eventually, having them perform the task with their eyes closed, or even utilizing stroboscopic goggles for vision obstruction could help to improve proprioceptive awareness while decreasing the reliance on visual feedback.
Even an exercise as simple as a straight leg raise is repeated practice in explicit learning. We tell the athlete to squeeze their quads and focus on keeping their knee straight as they perform the movement. We are literally teaching the athlete to do the very things we do not want them to actually do when they return to sport – internal focus of attention and visual dependency to perform a very simple movement task. Instead, we can have the athlete perform the task with their eyes closed, utilize augmented or virtual reality to make the task more meaningful and specific to them, or use of an external focus of control such as a laser pointer or metronome to guide the movement.
The verbal cues we give are another thing to consider. When we give cues such as “bend your knee more”, we may be further contributing to the visual dependency and an internal focus of attention by forcing the athlete to look at how their body is moving in relation to itself. Giving a cue that shifts the focus outside of the body (“land on the markers”) may help free up some of the cortical resources for more complex tasks such as reaction and anticipation. Changing cues to have more of an external focus of attention has been shown to be effective in producing the desired movements and can help improve the motor learning process.
This goes for how we give instructions and feedback as well. Giving an athlete cues or directions such as, “when you land, land with equal weight on each leg, make initial contact with the balls of your feet, then sink down into your heels as you bend your knees and go into hip flexion” may be taking up too much processing power in the premotor cortex areas of the brain and then when they go to perform that task in an open environment, they are unable to respond to the field, ball, opponents, and teammates around them. In my own practice, I usually begin by giving a very simple instruction (“jump off the box and land on this line”), maybe perform a demonstration, and then I allow the athlete to perform the movement with their chosen movement pattern. This shows me what their preferred movements are and what needs to be coached further.
When we are working with athletes, often one of the more difficult things to do is to sit back and allow them to perform without constant feedback. We want to help them complete the given task perfectly, and feel that we are only doing our jobs when we try to coach up every tiny flaw. We should see the amount and the rate at which we provide feedback as a means of progression. Initially, it might be more beneficial to give more consistent feedback, but we should gradually limit the amount of feedback we give. One thing I like to do once an athlete is comfortable performing a task is asking them at the end of a set how they think they performed. When we ask them, “how did that go?” or, “how do you think you did?” we are helping to drive implicit learning and shifting the locus of control back to them and away from us.
When I was a youth soccer player, I distinctly remember having coaches who would miss all the good things I did and only come give me feedback when I made a mistake. I used to think to myself that I was so unlucky to only be seen when I did something wrong. Having been on the other side of things as both a coach and a physical therapist, I now see that my youth coaches most likely did see the good things I was doing, but only felt the need to help me with the mistakes I made. I still catch myself doing this sometimes. We want to help our athletes get better and so we search for mistakes that we can help them fix and improve. However, athletes tend to respond more favorably to positive feedback rather than negative feedback. It is far more powerful to an athlete to be told when they have succeeded and asked to replicate that. One way I like to utilize this in the clinic is by noticing a well-executed rep or movement and then saying, “that was perfect, do every one exactly like that one”. Giving feedback in this way not only provides the positive feedback they require, but also helps to drive implicit learning.
Typically, athletes are seen by physical therapists in a clinical setting while they are rehabilitating after an ACLR. There is a big difference between performing a movement task in the safety of a closed clinical setting and in the unpredictable, open setting of a field or court. Neuromuscular control deteriorates when the distractions of opponents or a ball are added, so we need to prepare athletes for that. The easiest and most obvious way to address this is to take the athlete onto the field for some on-field rehab where these other components are gradually added to the program. I am a big proponent of on-field rehab and see the benefit of it regularly with my clients. I also understand that this is simply not realistic for many, if not most physical therapists.
Other ways to better prepare athletes for the open environment are to add reactive training and cognitive dual-tasking. Reactive training can be as simple as a balloon toss, juggling a soccer ball, or accelerating, decelerating, and changing directions in response to a verbal or visual command or cue. Cognitive dual-tasking can be performed by having the athlete perform an upper body task (catching a tennis ball) while performing a desired lower body movement (side shuffling). I like to have the athletes I work with perform math problems or answer trivia questions while performing soccer technical work. Be creative!
Being aware of the neuroplastic changes that result from an ACL injury and subsequent ACLR can potentially make an impact on the rates of secondary injury we are currently witnessing. Don’t forget that we still need to get the athlete really strong prior to returning to sport, and being cognizant of how we can address these neuroplastic changes can help us to design a more complete and comprehensive rehabilitation and risk reduction program.
Blog Contributor: Nicole Surdyka is a Doctor of Physical Therapy, Certified Strength and Conditioning Specialist, and former NCAA Division-1 soccer player at Saint John’s. She currently owns her own Physical Therapy and Sports Performance practice in Los Angeles with her husband, Marc, who is also a Physical Therapist. Nicole specializes in the rehabilitation and risk reduction of soccer-related injuries and is passionate about keeping soccer players on the field and performing at their best. Reach out with any questions for Nicole on IG (@dr.nicolept), Twitter (@NSurdykaPhysin), or online (https://www.nicolesurdykaphysio.com).
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