Tag Archives: Concussions

Why is heading the ball so dangerous for youth soccer players?

young girl attempting to head an incoming soccer ball
Photo by Carson Ganci on THE42

I received my first concussion while playing soccer at 15 when I was knocked out by a ball that was “accidentally” punted directly into the side of the head. It seemed to me like this was one of the few, rare ways to get a concussion from the sport – an unlikely occurrence combined with an unusually aggressive impact. I was proven wrong, however, after I received two more concussions just from heading the ball – a frequently used technique involving seemingly mild impact forces. I have since come to discover that concussions, particularly due to heading the ball, are a huge problem for youth soccer players: currently, in the United States, youth soccer players aren’t allowed to start heading the ball until age 11 in an effort to reduce the risk of concussions. But how do headers cause so many youth concussions, especially when the speed of play is so much lower than for adults?

Physical vulnerability to concussion mechanics

illustration showing a head impacting a an object with arrows decribing the movement of the skull and the brain towards the object just before impact
Illustration of the movement of the skull and brain just before impact with an object. Upon impact, the movement of the skull decreases rapidly while the movement of the brain has a delayed response. Original image created for Wikipedia

In most sports, concussions are commonly caused by rapid acceleration/deceleration of the head that causes the exterior of the brain to crash into the interior wall of the skull, which is suddenly accelerating in a different direction. When headers are performed in soccer, this rapid acceleration is caused by impact with the ball, and the risk of concussion depends on both the acceleration of the head and the duration of the impact. The acceleration of the brain can be modeled by Newton’s Second Law (F = ma) for a given impact force F, and the resulting acceleration depends on the effective mass of the players head m, which depends on both the strength and weight of the players head and neck as well as their relative movement compared to the ball (which boils down to technique). This means that a major portion of the risk of concussion relies on the size, strength, and technical ability of the player, all of which have an inverse relationship with player age. So while the relative speed of play and impact forces may seem lower for youth players that can’t run as fast or strike the ball as hard as their adult counterparts, these factors are offset by their relative physical vulnerability.

Issues with injury recognition and response

Another factor contributing to the threat of concussions for youth players is their relatively low ability to recognise and respond appropriately to a brain injury when one occurs. Between 2008 and 2012, researchers observing elite female players aged 11 to 14 for 414 player-seasons (288 athletes were observed for a single season and 63 were observed for two seasons) discovered that 59 concussions occurred, with headers being the most frequent cause at 30.5%. In addition to this injury frequency, it was found that over half of these middle-school-aged athletes continued to play with symptoms after receiving a concussion. This is an additional a logistical problem for youth players, for as age decreases, athletes on average have less access to on-hand, qualified medical personnel and less of an ability to self-diagnose and respond appropriately to injury, putting them at increased risk for long term damage.

The Dangers of Using Your Head: The Biomechanics of Sports-Related Concussions

Anyone that has ever had the misfortune of banging their head know how painful it can be, but does everyone understand just how dangerous it can be? Concussions occur when the brain hits the interior walls of the skull, either due to a direct blow or a sudden start or stop. These brain injuries most often result in confusion, headaches, and loss of memory but more severe injuries can cause vomiting, blurry vision, and loss of consciousness. In rare instances, they can even cause a brain bleed and result in death. Repeated concussions can lead to neurocognitive and neuropsychiatric changes later in life as well as increase a person’s risk of developing neurodegenerative diseases like Alzheimer’s.

So, who is at risk for concussions?

Athletes sustain 1.6-3.8 million concussions every year in the US. They are most common in contact sports such as soccer and hockey, but the largest contributor is American football. Players are constantly hitting or tackling each other in football, and each impact risks serious injury for both individuals.

How does it happen?

It all comes down to conservation of energy and momentum. Newton’s second law states that an object in motion tends to stay in motion while an object at rest tends to stay at rest, unless acted on by an outside force. When player 1 starts to run, he has a set energy and momentum based on his velocity (speed). Once he hits player 2, he either slows down, stops, or bounces off in the opposite direction. However, the initial energy and momentum that he had doesn’t just magically disappear, it needs to be conserved so it is transferred to player 2. This means that player two will start moving in the direction that player 1 was initially running. This is how billiards is played: the energy is transferred from the pool stick to the cue ball and then to the intended solid or stripe.

However, injury occurs when player 2 or his head cannot move. This may be because he hit the ground or another player or even simply because his neck stabilized his head, but regardless, that energy still needs to go somewhere. When the head stops, the brain keeps going until it collides with the inside of the skull.

Fortunately, not every hit results in a concussion. The brain is separated from the inside of the skull by cerebrospinal fluid that can protect it from collision to a certain degree, so not every impact reaches the injury threshold. What that injury threshold is has become the focus of many scientific studies.

Finding the injury threshold

The search for the injury threshold is a vital one that could help in the development of more effective helmets and rule changes to the game that could keep players safe. Three factors are believed to dictate this threshold: linear acceleration, angular acceleration, and location of the impact. The linear acceleration is what causes the collision with the skull, as previously described. The rotation of the cerebrum (the bulk of the brain) about the brain stem can cause strain and shearing within the upper brainstem and midbrain, which control responsiveness and alertness (causes the confusion symptoms). Finally, certain areas of the brain are more susceptible to injury- like the frontal lobe, temporal lobes, and brain stem since they are near bony protrusions– so the location of the impact can have a major influence in the injury threshold.

While there is still no set threshold, one study was conducted in which 25 helmet impacts from National Football League (NFL) games were reconstructed and the resulting helmet kinematics measured. The study found that the heads of concussed players reached peak accelerations of 94 (+/-) 28 g (acceleration due to gravity-9.8 m/s^2) and 6432 (+/-) 1813 radians/s^2. A separate study focused on the location of concussions of football players and that resulted from specified linear accelerations, as seen in Figure 1.

While there is still much that needs to be learned about sports-related concussions and their long term effects on athletes, scientists are well on their way to understanding the biomechanics that cause them. The next step is using that knowledge to create better protective headgear and a safer game.

Locations of concussions and their linear accelerations.
Back: Case 13-168.71 g (1 concussion)
Front: Case 12-157.5 g, Case 2- 63.84 g, Case 6- 99.74 g, Case 4- 84.07 g (4 concussions)
Right: Case 11-119.23 g, Case 8-102.39 g (2 concussions)
Top: Case 9-107.07 g, Case 1- 60.51 g, Case 7- 100.36 g, Case 10- 109.88 g , Case 5: 85.10 g, Case 3: 77.68 g (6 concussions)
Location of concussions and their linear accelerations. Modified from Neurosurgery

To learn more, check out these links!

https://pubmed.ncbi.nlm.nih.gov/23199422/

https://pubmed.ncbi.nlm.nih.gov/23299827/