Artificial turf and soccer

Before I start writing out whether or not playing soccer on artificial turf (AT) leads to injury, I have to admit that this was a real learning experience for me. For years, I've been convinced that playing on turf leads to higher chances for injury. So much so, that I repeated that on at least three radio shows last summer, during the women's World Cup.

But, that's why I love science. It proves me wrong all the time, and reminds me about how little I really know. It's humbling, wondrous and informative.

Just like my recent blog post on heading and youth soccer, I will be linking to the abstract of various articles. If you would like access to a particular paper in it's entirety, tweet me at @AlzBlog101 and I would be happy to send it to you.

1. What is Artificial Turf (AT)?

It's a playing surface used for sports such as field hockey, soccer, american football, etc. AT is made of synthetic fibers that look like grass. However, for countries where maintenance of natural grass is problematic due to non-ideal temperatures, AT has proven to be an alternative.

2. How did the idea that AT leads to increase in soccer injuries start?

While there were probably anecdotal reports, the first study that examined this issue was Arnason et al. (1996) . They found that the propensity for injury increased on AT vs natural grass.

3. Were the Arnason results replicated by other studies?

No. There have been many studies that suggest that there is no difference between injury risk of AT vs natural grass. These can be found here --- Ekstrand et al. (2006), Steffen et al. (2007), Fuller et al. (2007), Aoki et al. (2010), Bjorneboe et al. (2010), Kristenson et al. (2013) .

In essence, almost all studies suggest that the risk for injury does not increase for athletes playing on artificial turf. It's important to note that the studies cited above cover the gamut from NCAA soccer players to professional footballers - both male and female. So, there isn't a bias in terms of the level that the game is being played.

Here's something even more surprising. There have been studies that suggest that playing on artificial grass may be linked to LOWER injury rates than natural grass. Those can be found here --- Ekstrand et al. (2006), Soligard et al. (2012), Williams et al. (2013), Almutawa et al. (2014), Meyers (2013).

4. Okay, so playing soccer on AT is better than on natural grass?

Not so fast. You see, the articles cited above look at injuries as a whole. It's still possible that there are differences in particular injuries. A good analogy is that the articles above are looking at the injury issue at a whole-forest level. Whereas, in order to understand the risk for specific injuries, we have to go down to the tree-level.

5. Have there been studies that look at specific injuries in terms of artificial turf?

Yes.

6. What did they find?

The big one is that AT seems to be bad news bears for your ankle! Ekstrand et al. (2006), Steffen et al. (2007), Ekstrand et al. (2011) all found that playing on AT leads to an increase in ankle injuries in soccer players. For the sake of completion, it is important to note that Soligard et al. (2012) found the opposite - a reduction in ankle injury in soccer players playing on AT.

Hagglund et al. (2011) found that there was no difference between AT and natural grass surface for risk of patellar tendinitis (that's a fancy way of saying pain caused by inflammation in the knee).

Ekstrand et al. (2011) found that male soccer players were less likely to have a quad injury when playing on AT vs natural grass.

7. Woah! Getting too much. Summarize this for me.

Essentially, there is no increase in overall risk for injuries when playing on artificial turf vs natural grass; in fact, some studies suggest that it may be better overall than grass. However, there's general consensus that playing on AT may be a risk factor for ankle injuries, in particular. So, watch those ankles, friends!

8. So why does this myth about AT persist?

There are some general reasons - such as the naturalistic fallacy - where people believe that just because something is natural, it is automatically better than something synthetic or artificially manufactured.

Another reason is that we tend to extrapolate results from other sports into soccer. A perfect example of this is comparing football injuries to soccer. Both can be played on AT and therefore, when we see a study that suggests that injury X is increased in football, we assume incidence of injury X is also increased in soccer.

However, the sports are drastically difference and this assumption isn't necessarily true. For example, Balazs (2015) performed an examination of the literature, and found that playing on AT results in an increased risk for anterior-cruciate ligament (ACL) injuries in american football, but not soccer players. Therefore we should be careful to not over-interpret data seen in other sports played on AT.



So, lesson learned from my perspective - always fact-check everything. Especially things that I "know" are true.

Heading in youth soccer: what the science says

Recently, the United States Soccer Federation (USSF) released a report advising the elimination of heading in soccer for kids under the age of 10. And recommends that full-contact heading not be allowed till athletes get to 16 years of age.

Now, while everyone is on board with the idea that player safety is very important, particularly that of children and young adults, there has been much debate over whether the guidelines would benefit athletes and soccer in the long-term.

Let me start by saying that I believe that concussions in soccer are a serious, serious, serious, serious, serious, serious, serious concern. Is that serious enough? I believe that concussions are currently being managed incorrectly by the Football Associations and FIFA. And that things need to change rapidly so that our soccer players can live a healthy life after they retire. However, today, we will be focusing on the topic of concussions in youth soccer players.

While one can have a myriad of personal opinions on this topic, and certainly, I do, too (I'll discuss those later), the majority of this post will look at what the scientific literature says re: Heading in youth soccer. I understand that many do not have access to the articles I'm citing here, so I will link to the abstract (which is available to all), and if you are interested in a particular article, tweet at me, and I'll send it to you.

1. Can heading the ball lead to concussions in high school players?

Yes. It isn't the most common form of concussive injury in youth soccer players, but, it is certainly possible (Cornstock et al, 2015 ). However, what this study does not look at  is HOW those ball-to-head related concussions were procured. That is a key caveat to this study.

There is another study that suggests that zero concussions were produced by heading the ball correctly, and all were a result of the ball striking an unprepared player at close distance (Boden, 1998) .

2. Can heading the ball lead to concussions in youth soccer players?

Doesn't seem like it. Here's a key excerpt from a book chapter  ---

"Dr. Kirkendall . . . calculated the impact of a soccer ball on the head of youths of various sizes, based on the likely speed of the ball, and concluded that the force of impact is well below the force that is thought to be necessary to cause a concussion in heading a soccer ball." --- Dr. Donald Kirkendall, Causes of head injuries in soccer .

Even in U14's soccer, there is likely not enough ball velocity to cause concussion (Hanlon and Bir, 2012) .

A meta-analysis (looking at various studies between athletes 10-24) suggested heading the ball was unlikely to cause injuries (Pickett et al., 2005).

Essentially, those kids do not kick the ball hard enough to cause the G-forces (acceleration forces) to result in concussive injuries.

3. What about subconcussive injuries from heading?

In order to answer this, a quick primer on subconcussive injuries: It is an emerging area of research that suggests that repeated impact to the brain can result in brain damage, even though concussion hasn't occurred. The problem with studying subconcussive injuries is - how do you tell if someone has one? Neuroscience tackles this in a couple of ways. Firstly, we have identified certain biomarkers (biological red flags) to suggest if someone is exhibiting hallmarks of disease. The second technique is to look at behavioral tests that suggest whether someone is cognitively impaired. The assumption being, in both cases, if subconcussive injuries have occurred, there will be a biological (biomarker) and/or behavioral (neurocognitive) change.

Coming back to the original question. Most literature suggests that heading the ball does NOT lead to changes in biomarkers/neurocognition. These can be found here --- Kontos et al. (2011), Stephens et al. (2005), Kaminski et al. (2007), Broglio et al. (2004), Guskiewicz et al. (2002) and others.

But, this study, does suggest that a cognitive change may occur - Zhang et al. (2013) . I have to state a caveat - this Zhang study is poor. The effect size (how different the soccer-playing and non-soccer-playing groups were from each other) is very small. For my science friends - they set a non-one sided gaussian t-test alpha of 0.1, which is an immediate red flag. For my non-science friends - I think the effect they observe is not worth believing.

4. Okay, that's a lot of words. What's the gist?

Currently, a preponderance of the literature does not support the idea that heading the ball leads to subconcussive injuries in youth (kids - high school) soccer players.

5. Is that a definitive no then?

Not quite. You see, the work surround subconcussive injuries is nascent. And, as such, has caveats. For example, some of the behavioral tests and biomarker tests need further validation. Therefore, it is theoretically possible that subconcussive injuries ARE occurring, but our tests aren't well enough designed to detect them... just yet.

6. What about the report of the kid who almost died after heading the ball?

That's a real report. That happened a few years ago, and no one has contradicted the young man's claim that his subdural hematoma (potentially fatal bleed in the brain) was the result of a single header (Lutfi et al., 2009). My concern is that the report says he headed the goalkick with the "front" of his head. I am not sure if this means with his forehead (which would be the correct way to head the ball), or with the top of the head (incorrect, and unfortunately seen in young soccer players who haven't practiced heading).

7. What about player to player contact?

Yes, this often is the culprit for concussions. Most of the articles I've linked to above suggests the same. These injuries can be a result of two players going for a header, or accidental contact with one player's knee, while the other is on the ground, etc. There are a myriad of ways that player to player contact can result in head injury and concussion.

Head to head injury is a serious concern

Okay, now we are going away from the realm of scientific literature into my own opinion (using the literature I've read as a basis, of course)

8. So, what's the solution?

In my opinion, there should be a serious punishment for serious player to player contact. In the last 3-4 years, the concept of "out of control" tackling has come into play.

You see, while I was growing up, the definition of a good tackle was "getting the ball". If a player got the ball before he made contact with the player, it was deemed a good tackle - regardless of whether this involved excessive force or injury to the opposing player. However, now, even if a player wins the ball, if he comes in with excessive force, tackles from behind or uses two-feet, the referee usually punishes the tackler with a red card (FIFA, law 12) . Why? Because all of those conditions are optimal for causing injury.

Similarly, excessive force, using elbows, out of control contact with an opposing player's head (knee-head, for example) should be deemed dangerous play, and therefore a red card. This would result in players being careful of so-called 50-50 balls, and wary of using their elbows as leverage.

9. But, what about heading itself?

I respect people's opinion who think "well, removing heading in youth players won't hurt". But, in my opinion, having young kids learn how to head the ball early would lead to developing the appropriate neck muscles needed (Gutierrez et al., 2014) to prevent head injury in the future. If heading the ball isn't being introduced to them until they are 14, this may lead to an INCREASE in the number of concussions. Because, by the time they're 14, they are kicking the ball much harder, and have yet to learn the basics of heading.

Incorrect way to head the ball. (Image via http://hubpages.com/sports/Soccer-Head-Injuries-in-Children-Brain-Damage-from-Heading)

10. To summarize:

1. Preponderance of scientific literature does not support the idea that heading can lead to concussions or subconcussive injuries in soccer players.
2. More work needs to be done.
3. In order to minimize concussion, new rules regarding player contact need to be made.