This is a concept that makes a lot of sense to me and I was first introduced to this ~6 years ago. A lot of this initial work comes out of Australia and is a deep dive into the mechanism for non-contact ACL injuries. We know from the research that ACL injuries occur from non-contact (where there is no contact with an individual or object resulting in the ACL injury) and a contact injury (where there is contact with something or someone that results in the ACL injury). An example of the non-contact ACL injury is when a player has a rapid change in direction and their knee goes into a dynamic valgus and they rupture the ACL. An example of the contact ACL is a another player strikes the knee of an opponent and this ruptures the opponents ACL. We also know from the literature that the majority of injuries are non-contact in orientation (70-80%) and these are the ones we can impact the most with screening and injury prevention techniques.
However, there is also another category of ACL injuries called indirect contact. This is where there was contact with the athlete prior to landing and their change of direction. As an example, a soccer player goes up to head a ball (pictured). The player in the red jumps for the ball. In the higher centers in his brain, there is a motor plan that his brain resorts to for effective execution of that motion. For this to work efficiently, his body is in a certain position and he lands with his legs and center of mass in a predictable position. However, what happens, as he heads the ball is that the player in the blue strikes his shoulders in mid-flight. This drastically alters where he lands, where his center of mass is relative to his legs and his feet may not be in the optimal position. When he then changes direction to run after the ball, his body is in the wrong position and he ends up falling into a rapid dynamic valgus and ruptures the ACL.
In a study by Stuelcken et al J Sport Sci 2016 the authors performed a systematic video analysis of 16 anterior cruciate ligament injuries sustained in elite level netball players during televised games. Of the 16 injuries, 8 of these were identified as indirect contact ACL injuries. In the indirect contacts a player was jumping in the air to receive or intercept a ball when they received a perturbation in the air. As a result, the athletes landing was unbalanced resulting in excessive loading to the knee that was ultimately injured.
This concept of indirect contact is new to many but it has been a concept that has been investigated for the last 10 years. We know that we can create preventative programs to aid in reducing non-contact injuries but is there any form of training that can be done to aid in prevention of indirect contact injuries. Absolutely!
One concept we talk about a lot with our certification course is the concept of rapid neuromuscular response or RNMR. With this approach to training, we want to teach to the athlete to have a rapid neuromuscular response to external stimulus (indirect contact). This response should be one that results in stability and full kinetic chain stability. In order for this form of training to work, we must first talk about the concept of perturbation training. This is a technique that we often employ in rehabilitation but which is rarely used in performance training. Frankly, there is application in both settings if it is done correctly.
Before we do a deep dive into the training, we must first talk about how perturbations should be done. When I teach this in our courses, I see a lot of different ways that perturbations are applied. Keeping in mind, the goal we are looking to achieve is a rapid neuromuscular response to provide stability to the stimulus applied. So, our stimulus, perturbation, should not be so great that it breaks the athlete resulting in movement. We are looking for stability.
An example pictured here. I have an athlete in a lunge position and hold their arms out in front of them, palms together (pushing palms together to bring in pec contraction) and asked to stabilize their shoulders, core and LKC. I ask them to not let me move them. I provide perturbations with my hands to their hands, shoulders and knee. My perturbation (or force) does not exceed their ability to stabilize. I want train a motor pattern that results in them stabilizing versus allowing the body to move with the stimulus. These are two very different motor patterns and for prevention and ability to resist indirect contacts, we have to teach to stabilize when these occur. This is one area where I see a lot of folks make a mistake. The force they provide is greater than the athletes ability to stabilize so they are essentially teaching them to break instead of stabilize. As the athlete improves, we obviously provide more and more force but initially we are looking for the rapid response for stability.
Next week, we will dig a little deeper into this concept of rapid neuromuscular response and how we can train this from simplistic to ballistic movements. Stay tuned as I am super excited to share with you. Have you followed my instragram @bjjpt_acl_guy lately? If not, you are missing out. I am constantly posting the latest research in injury prevention and sports medicine. Don't miss out and please share with your colleagues, athletes and training partners and please be sure to follow us on instagrm @ bjjpt_acl_guy and twitter @acl_prevention. Train hard and stay well. #ViPerformAMI #ACLPlayItSafe