“ACL injury prevention strategies for any coach” by Neil Welch, Head of Rehabilitation at SSC Sports Medicine
This article was published by Sportsmith.
The Sports Surgery Clinic (SSC) in Dublin performs around 1,000 anterior cruciate ligaments (ACL) reconstructions per year. I lead SSC’s Lab services, which performs biomechanical and performance testing for the majority of these athletes throughout their rehabilitation. In my role, I interact with a large number of athletes who have undergone surgery, so I understand the massive physical and emotional challenges that are involved in the athlete’s rehabilitation process.
This perspective has shaped my thoughts around injury prevention concerning change of direction and agility training. Hopefully, this article will provide you some ideas of why and how you can implement strategies to reduce the risks of ACL injury that your athletes face during changes of direction.
Movements and positions that increase ACL risk
Before we try to implement injury prevention strategies, we should try to understand the mechanism of ACL injury and whether it relates to the sport we work in and the athletes we work with.
In invasion sports, ACL injury occurs most commonly during non-contact change of direction tasks in both attacking and defensive scenarios. ACL injuries result from excessive rotational loading through the joint causing strain and shear loading high enough for the ligament to rupture. The impact in the majority of circumstances is a year or more out of action.
Researchers have identified a number of biomechanical or technical factors that increase this rotational loading through the knee. To reduce these loads, we need to know what these factors are.
Wider foot plants, greater angles of hip abduction, greater foot external rotation, greater ipsilateral trunk sway and greater knee extension all relate to increased rotational knee loads. Away from the biomechanical factors, there are also performance factors that contribute to increased knee rotational loading during change of direction. These are greater velocities, greater ground reaction forces and greater angle of cut. Conversations regarding the performance-injury trade-off centre around these considerations.
What technical changes could lower an athlete’s risk of ACL injury?
The video below shows a rugby 7s player injuring her ACL. The player in red attempts to decelerate and cut immediately to her left using her right leg, and then step inside the #6 in white. She ruptures her ACL in this stride. Extended knee, ipsilateral trunk sway, large ground reaction forces, high velocity movement and large angle change. A mix between the technical and performance factors we mentioned above.
If we are to prevent this injury, we need to reduce the loading through the joint.
However, from a performance perspective, reducing velocities and ground reaction forces is not what we’re about. In fact, it’s the opposite. The sharp angle of cut is required to evade her marker and is an important attacking option, so that is also not something we’re going to change. Even if it were, can you imagine telling your athletes you are going to slow them down when they cut? Instead, we have to look at what technical factors we can influence.
Video 1: Deceleration example
In the example above, the technical changes we need the athlete to make are reducing trunk sway and using a strategy with more knee bend while decelerating. If we think of a technique change that would achieve both, lowering the centre of mass would fit the bill. The excess trunk sway that contributes to the rupture in this instance happens because the athlete creates an axis of rotation about a stiff limb out in front of her as she decelerates. Think of how a pole vaulter drives the pole into the box. Except in this instance, the pole (or the knee) gives way.
Expanding our view to the full range of technical factors, lowering the centre of mass will influence many of them. A wider foot plant and greater hip abduction is not necessary to apply force horizontally into the ground to change direction if the centre of mass is lower. This, too, will reduce rotational knee loading. A second ACL injury technique risk factor, trunk sway, often occurs when the athlete enters the cut with a vertical trunk. A vertical trunk creates a greater moment with a longer lever. Therefore, we can shorten the lever arm and reduce the moment with some trunk or hip flexion (leaning forward on the approach), lowering the likelihood of the trunk swaying.
Ultimately, greater hip flexion and knee flexion, or being closer to your athletic stance, will reduce rotational knee loading during the cut.
This does not mean that we need to be coaching our athletes into deep squat positions during and approaching change of direction tasks. A better way to think of it is that the further you deviate upwards from your athletic stance at every stage of the cutting task, the greater the risk of injury.
Our injury prevention strategies should seek to create stable attractors away from this very upright strategy.
Prevention & performance: Trade-offs we won’t make
A major concern for performance professionals when we talk about injury prevention is the potential for negative effects on performance. Some research suggests reducing knee loading by using strategies such as softening landings to reduce ground reaction forces [6] or planting the foot close to the centre of mass during a cutting movement 7). These conclusions follow from the sole intention of reducing knee loading without considering the impact on performance.
Research results and conclusions like these contribute to the performance-injury trade-off conversations. If we consider these suggestions from a performance context, deploying softer deceleration strategies would increase deceleration time; and applying force horizontally into the ground is necessary for enhanced cutting performance [8,9].
But what does the performance-oriented literature have to say about cutting biomechanics?
Leaning and rotating the trunk in the direction of the cut, maintaining a lower centre of mass and resisting movement of the centre of mass towards the plant foot (think lateral stiffness) are all associated with a faster cut. These factors are the opposite of the technical risk factors for ACL injury we discussed above. When you add in that short ground contact times and early force production are also associated with faster cuts, both of which require greater pre-activation and/or co-contraction – which may also be protective – you may start to think, as I do, that performance and injury prevention are not mutually exclusive.
If you address injury prevention appropriately in cutting, it should also improve performance.
Assessing tactical and in-game scenarios for ACL risk
Assuming you buy into my technical factor reasoning (and it’s fine if you don’t!), the next task is to identify the risky scenarios in your sport so you can target them. This is worth considering because they do vary.
In football (soccer), the majority of injuries occur during a defensive press [1], so strategies to reduce risk amongst a playing squad can be targeted for those scenarios. In rugby, 46% of the non-contact injuries occur during attacking cuts – by far the largest proportion – and 21% in defensive pressing and tackling situations [2]. Jumping and landing is more prevalent in AFL, where 37% of non-contact injuries occur during sidestep actions, with 32% and 16% occurring in landing and land and cut actions, respectively.
If American football is your sport, 70% of injuries are non-contact (higher than I would have thought), with 86% of them occurring in cutting, deceleration and running. Of these, 36% were in attacking actions and 44% were in defensive actions [4]. That’s a more even spread across attacking and defensive scenarios than in soccer and rugby. Recent research in basketball found that players with a higher tendency to drive to the basket were at greater risk of ACL injury [5].
Insights like these allow us to improve the targeting of interventions, not only to certain situations but also towards certain players. However, this research is still new. If we’re taking an individual approach to targeting interventions, we need to take a similarly individual approach to identifying which athletes to target. And before all that, we have to decide if we should intervene at all.
When should coaches introduce ACL prevention training, and with whom?
There’s nothing wrong with questioning whether you should implement a preventive strategy.
You may feel that your playing group, by virtue of their competitive or experience level, have some degree of resilience to ACL injury. You may feel that those with risky strategies have already been injured earlier in their career, and have either rehabbed and are back playing or they didn’t make it to that level. You may, therefore, question whether prevention-based interventions are necessary. Your time and your athletes’ time may be better spent on other activities.
An athlete’s stage in career may also play a role in your thought process. Athletes who are approaching the final years of playing may not be best served or even be interested in prevention work. You may also decide that there are higher priorities and that you should invest your time and energy elsewhere within the performance and medical program.
Alternatively, you may opt to use a broad brush approach. This entails applying the same program elements across your entire playing group. This is particularly beneficial if you are working with younger or more novice athletes, as there is likely more room for improvement. If you’re the only coach who will be implementing the program, then this approach is easier on your time than trying to target smaller groups or individuals. This approach also helps you be consistent in your messaging and the way you coach. If you’re part of a larger setup, the entire coaching staff needs to buy in with time and training to ensure consistency in delivery from all the coaches to all of the athletes. Otherwise, you run the risk of the messages diverging from coaches to athletes.
For example, you may decide that to help reduce external foot rotation during cuts you want your athletes to perform their lifts in the gym with a neutral foot position.
How many coaches do you have to get on board with that simple message? How many athletes who have previously done it another way do you have to sell it to, now that you are changing tack? Does everyone buy in enough to make that change?
It can be harder than we first think to implement these changes to a large program or playing group. Another possible downside is that you may be wasting the time of those athletes who already excel in this area. They may be better served addressing other elements of their game.
Finally, there is the targeted approach. This is where you identify certain individuals or groups of players to work with specifically to address their deficiencies. There are a number of ways you may decide on these groups.
Given that increased velocities and ground reaction forces increase risk, you may want to take a closer look at some of the younger players transitioning into the senior setup who are not used to playing at that intensity. Similarly, you may have new athletes joining from another organisation who may be used different tactics. At a soccer team, for example, if a strong defensive press is a large part of your tactical approach and an athlete is joining from a group where it was lemphasized less, they may be a target of your intervention.
Athletes who are exposed to the risky scenarios in your sport more frequently may make the list. In rugby, where attacking sidesteps are the riskiest scenario, you may work with the players for whom an attacking sidestep is an important part of their game.
Certain drill types can serve as a screening tool. One-on-one contests to pick out the athletes with high levels of trunk sway or possession games to find the upright decelerators are some other valid approaches.
Coaches need to develop their observational skills if they are using this approach, along with having a close relationship with the performance analyst. Coaches can also identify players with risky strategies by watching training or game footage of certain scenarios.
Three areas for ACL injury prevention interventions
If you have decided that a change of direction-based intervention is something you want to pursue and that you have athletes who would benefit from it, then what do you do? Obviously, the answer here is that it depends.
Broadly speaking, the aim is to form a stable attractor around your athlete’s ability to get into and out of their athletic stance at every stage of a change of direction. It’s as simple as that. In defensive scenarios and at slower speeds, this athletic stance will be lower than at higher speeds and in attacking cutting actions (see Kobe Bryant clip below). They need to be able to do it forwards, backwards, sideways and in rotational movements, and move seamlessly between them all. They need to do it from stationary starts and while moving at speed. They need to be able to express large amounts of force rapidly as soon as they hit those positions. In attacking situations, and during higher velocities and shallower angles, the athletic stance will be more upright but should still have some level of hip and knee flexion.
There are many options that we can implement to form these stable attractors, reduce risk of ACL injury and improve performance during cutting. We can approach them via three broad, practical programming areas.
Coaches need to develop their observational skills if they are using this approach, along with having a close relationship with the performance analyst. Coaches can also identify players with risky strategies by watching training or game footage of certain scenarios.
Three areas for ACL injury prevention interventions
If you have decided that a change of direction-based intervention is something you want to pursue and that you have athletes who would benefit from it, then what do you do? Obviously, the answer here is that it depends.
Broadly speaking, the aim is to form a stable attractor around your athlete’s ability to get into and out of their athletic stance at every stage of a change of direction. It’s as simple as that. In defensive scenarios and at slower speeds, this athletic stance will be lower than at higher speeds and in attacking cutting actions (see Kobe Bryant clip below). They need to be able to do it forwards, backwards, sideways and in rotational movements, and move seamlessly between them all. They need to do it from stationary starts and while moving at speed. They need to be able to express large amounts of force rapidly as soon as they hit those positions. In attacking situations, and during higher velocities and shallower angles, the athletic stance will be more upright but should still have some level of hip and knee flexion.
There are many options that we can implement to form these stable attractors, reduce risk of ACL injury and improve performance during cutting. We can approach them via three broad, practical programming areas.
The second area you can improve in the gym is technique and capacity during unilateral deceleration. Coaches often overlook cuing the speed of deceleration, particularly in landing tasks where we instead focus on “stability.” Instead, if we cue the landing to be quick, the stability comes with it and you’re also developing early rate of force development qualities within your athletes.
You can also develop good technique habits of linking hip/trunk and knee flexion, starting the move move away from vertical trunk decelerations.
Third is your plyometric work, and moving to incorporate triple flexion in both vertical and horizontal explosive work. Some triple flexion prior to ground contact helps the athlete form habits around safer positions. Drop squat patterns can breed familiarisation with the techniques you want to develop before progressing to drop jumps and lateral rebounds. This differs from the standard approach to plyometric work in the positions athletes are coached into when they interact with the ground.
Multi-task with warm-up themes
The next area you can use to address injury risk is the warm-ups. With warm-ups, you can use the broad brush and targeted approaches alongside each other.
Implementing more challenging movements allows you to be inventive and gives you the opportunity to do some really fun coaching, but requires a little more organisation.
How you chunk these movements and drills is up to you, and may be dictated by the needs of the sport.
Creating themes for drills though will allow you to be a bit more targeted in the areas you want to address.
One theme could be transitions, where you challenge the athletes with the direction and positions of movements. For example, side shuffle movements into a forward run where you are trying to improve the fluency of movement in athletic stance positions. Another theme could be around backwards movement, an area in which I’ve found athletes to be generally poor. When was the last time you coached someone to run backwards? Athletes get injured when transitioning out of backward movements because they put themselves in poor positions. A final theme you might lean on is around shadowing and trying to develop perceptive and transitional skills together. To be even more targeted in this approach, pick your athletes one at a time to cue on positions or movements. This is why I said the organisational elements in your drills is important, as you can then spend your time observing and coaching one-on-one between reps.
The added value that runs through all of those themes is that you improve defensive movements and enhance performance while also addressing some of the risk scenarios for ACL injuries.
Integrating tactical, technical and physical programs
The final area where you can make an impact is somewhat dependent on your coaching environment and the access you have to your athletes within sessions. This is around specific technical/tactical scenarios. It may be that this actually becomes a warm-up theme if you are unable to get space within a session itself. Or, you can link the warm-up theme to the scenario and have a targeted training block.
For example, if your scenario is around improving defensive pressing then you may focus your warm-ups around transitions from forward into lateral movements. In an ideal world, you would present this theme to the athletes as an aim of the training block with performance analysis support and consistent delivery of message between technical, S&C and medical staff. However, you may also be on your own with only a few minutes a week to devote to this. That underscores the importance of consistency throughout the program as a whole. If you combine the influence of your gym and pitch warm-ups, the patterns within your lifts and explosive elements in the gym and any scenario-based work you are able to get in, then it is possible to make a large impact in these areas and you will see them transfer onto the pitch.
Proactive approaches to injury prevention
On the subject of transference, yes, all these programming and technical interventions transfer to the sport. But it takes time, consistency and perseverance on the part of you, the coach. I remember watching a game with a GAA team I worked with early in the second season and seeing a defensive situation where all of the players involved were in the positions we had been working on in training. It seems a small thing, but it was the first example with that group that clearly showed we were making an impact. During a four year stint, we had no ACL injuries.
ACL injury prevention and performance improvement are not separate entities when we consider change of direction and agility. Coaches have the opportunity and ability to improve both simultaneously.
If you manage to prevent an athlete from going through an ACL injury experience, they will never be able to thank you and you will never know who you have helped. But it is possible and worth trying.
