Leah Williamson, Beth Mead, Vivianne Miedema, Laura Weimrothier – these are all women footballers who don’t just have the club they play for in common. They have all suffered an injury to their ACL (Anterior Cruciate Ligament) in the past twelve months. It wasn’t just these unlucky four Arsenal WFC teammates that fell victim to ACL injury last season; they join a growing list of at least 25 other women footballers across the world’s top football divisions who have injured their ACL this season. With their injuries coinciding with the run-up to the Women’s World Cup this past July and August, it’s easy to understand why women footballers and their clubs are anxious to get to grips with solving this epidemic, so they need not miss out on big international competitions and spend time watching their teammates on TV at home.
What is an ACL injury?
An ACL injury is an injury to the anterior cruciate ligament that sits across the middle of the knee joint. This happens when the ligament is overstretched and as a result tears. This tear can be partial or complete.
What do we currently know about ACL injuries?
This type of injury tends to be sustained during non-contact segments of a football game, such as landing awkwardly from a jump, preparing to push off to sprint or using your legs to break speed after running at pace. Each of these scenarios can lead to something known as knee valgus – the inward or outward turn of the knee. Knee valgus puts unnecessary stress on the knee joint, overstretching the ligaments in the knee. ACL injuries are also said to be due to underdeveloped knee muscles around the knee joint which cause an imbalance in the quadricep to hamstring muscle ratio in the upper leg. This is seen especially in women athletes (Sutton et al., 2013). This muscle imbalance ends up putting unnecessary stress on the knee joint as the impact of running, jumping, landing etc isn’t shared equally by these different muscles around the knee.
We also know that ACL injuries are becoming alarmingly common at all ages and all levels of football and physical activity. Orthopaedic surgeons have reported that there has been a 29-fold increase in ACL rupture surgeries in children since the late 1990s (Nogaro et al., 2020). Increasing numbers for surgery after ACL injury are particularly being seen in young girls and women. Such an increase is being linked to a couple of key contributing factors. One being the transition from sedentary to active lifestyles. While there is said to be more support for injury prevention and recovery for boys and men compared to their female counterparts. That being said, orthopaedic rehabilitation specialists have said that there is a distinct gap in knowledge in the UK about ACL injury prevention programmes in both boys and girls sport, including information on adequate warm up techniques for young people – which is another key factor contributing the surge in ACL injuries. Including stretches and muscle activation activities at the start and end of intense physical activities like football is thought to reduce ACL injury risk by 50-70%.
Watch this video for more information the rise of ACL injuries in youth sport.
As it stands though, there is interesting evidence to suggest that ACL injuries aren’t purely an injury that can be solely attributed to the leg muscles around the knee or some of the psychosocial issues mentioned in the video above. Startlingly perhaps, the brain is also starting to be considered in the ACL injury equation.
What role does the brain play in ACL injury?
There are receptors in the muscles, ligaments and tendons of the knee joint that respond to movement and tension in the muscles (called muscle spindles and Golgi tendon organs). These receptors send messages about the knee’s position to the brain and the rest of the nervous system. It’s possible that a mix up in these signals could sometimes contribute to ACL injury. One such mix up in messages can come from disruptions in attentional focus- where players on the football field choose to direct their attention.
One difficult thing about football is that players’ attention is constantly pulled in many different directions. As you are dribbling up the wing, should you focus on the call from a team-mate you could cross the ball to, the approach of a defender you want to avoid, or the pain in your tiring muscles?
All the different sensory inputs a footballer could attend to on a football pitch compete for importance in the brain, requiring a huge amount of cognitive effort to sift through. During these times of high cognitive demand, the body – muscles around the knee joint and in the lower leg, are forced to quickly respond to a player’s chosen movement pattern. Doing so at high speed can place unnecessary and unexpected stress on the joints and muscles i.e. the muscle spindles have to produce contraction unexpectedly. This process happens too quickly to allow for the muscle spindles to prevent the muscles being stretched outside of their normal range. So, at times, this unexpected stress on the knee joint increases the possibility for knee valgus and ultimately puts footballers at greater risk of ACL injury.
ACL injury in both men and women footballers has also been linked to difficulties with the brain being able to integrate information from the sensory system (e.g. eyes) and then translating this information into successful movements. For successful movements or skills to be performed in football there needs to be an accurate reception, interpretation and organisation of the information that is fed to the brain. A slowing of this process due to high task demands leads to a delayed response from the muscles required to perform certain movements/skill. This delay in information delivery can in turn increase the load that is placed on muscles that are not prepared for upcoming movement, leading to joint instability and again, increasing the risk for players to damage their ACL.
How does ACL injury affect the brain?
The brain has the ability to change in response to the environment and the conditions it finds itself in. This property of the brain is called neuroplasticity. As such, any injury has potential to change the brain’s structure and function. For example, after a tear to the ACL, the brain has to adapt to the loss of input from receptors at the knee joint. Due to the disruption of messages sent from the knee joint to the brain, the brain sends less efficient and coordinated messages back to the knee, leading to a change in the subsequent movements made by the knee. Footballers who have injured their ACL, like Simone Magill (Northern Ireland and Aston Villa Striker) have reported how difficult it is to learn to walk again after an ACL tear, while coming to terms with having to retrain her brain to control the movement of her knee and lower leg.
The change in messages from the ruptured knee joint to the brain and vice versa causes brain restructuring via a mechanism known as cortical reorganisation. Maps within the cortex reorganise and restructure based on the changes to the information sent to this area of the brain, creating a new map for the associated movements like walking, running, passing a ball, jumping for a header, shooting at goal and the cognitive processes that accompany these movements. For example, there is reported to be more activity in frontal regions of the cortex during knee flexion-extension cycle, suggesting that it takes more cognitive effort to make less efficient movement patterns during rehab after injury (Grooms et al., 2017). This can change again after reconstructive surgery as the knee learns to make new movements with the new messengers involved, in turn, changing the cortical map.
How can we leverage the power of the brain to assist with ACL injury rehab?
There is strong evidence to suggest that training of cognitive functions like attention, vision, and working memory during rehabilitation after ACL injury improves outcomes in footballers (Kapreli et al., 2009). One research group has looked at how changing where footballers place their attention, either away from the body (external focus of attention) or internal to the body (internal focus of attention) has an impact on the kinematic measures associated with good recovery outcomes. Encouraging athletes to have an external focus of attention allowed for significantly larger knee flexion angles upon initial ground contact, higher peak knee flexion, bigger range of motion at the knee joint and shorter times to reach peak flexion of the knee joint (Goekeler et al., 2015) compared to those who used an internal focus of attention. Examples of using an external focus of attention in football training during skill practise would look like asking players to focus on different things in their environment rather than on their specific body movements. For example, focussing on pitch markings or cones, ball stitching etc. Goekeler and colleagues in their study, had participants focus on the surface they were jumping off from and landing on by saying “Jump as far as you can. While you are jumping, I want you to think about pushing yourself off as hard as possible from the floor.”
The use of vision-based techniques in ACL rehabilitation also has a positive effect on rehab outcomes (Wohl et al., 2021). Training performers while administering small disruptions to their vision during movement tasks that involve the lower limbs can train the brain into prioritising the connection between the brain and the muscles over the more game strategic aspects of a football game. Practically, the small disruptions in the rehab process can be created by fitting the player with stroboscopic or prism glasses that distort the wearer’s vision. Such distortions force the brain to adapt to the information available and work out new movement solutions to overcome the disruption in the information it receives from the eyes to find success. This results in a reduced need to rely on vision to perform the tasks, and in turn increases the efficiency of the communication between vision, muscles, and the brain.
Importantly, including warm-ups at the start of football sessions, for both youth and adult players, is not just good for warming up and loosening players’ muscles, but also crucial for the brain. Warm-ups help to prepare the movement sequences represented in the brain that are needed to perform football skills successfully during practise and matches. Preparing the brain to perform certain movements ahead of jumping straight into sport makes sure that the movement representations are easily accessible at the very moment they’re required.
While it is important to focus on the mechanisms behind ACL injury to prevent its occurrence in the first place, perhaps a more brain-centred approach to prevention and subsequently rehabilitation could bring positive change to the current state of play with ACL injury in women’s football. By combining the methods mentioned above, focusing on leveraging the power of the brain and introducing training techniques into football training, we not only aid players in a more efficient return to the sport they love but also add to the toolkit needed to prevent ACL injury.
Cover Image: Milad Fakurian via Unsplash