The Safety of Artificial Turf vs. Grass as a Sport Playing Surface

I was interviewed last week for a newspaper article which looked at the debate over a local school’s intention to transform a grass playing surface to artifical turf.

Among the controversies in sports medicine, the turf vs. grass wars are not the loudest nor the meanest, but they have been among the most persistent ever since 1966, when the Houston Astros first introduced a synthetic turf playing surface in the Astrodome, and dubbed it Astroturf.

Picture_of_Reliant_Astrodome

Reliant Astrodome

The history of the Astrodome makes for interesting reading:  of note, the original intention was for the surface to be natural grass, and the makers of the dome had installed traslucent skylights to allow for grass to grow on the indoor surface.  Alas, not enough light made it to the playing surface, the grass died, and Astroturf was born.

The progress of science and technology have seen Astroturf give way to newer, so-called second-, third-, and even fourth-generation turfs. The  sporting world has even demonstrated that an indoor venue can sustain a natural grass pitch: witness the luminous Forsyth Barr stadium  in Duenedin, NZ, which has hosted matches from the 2011 Rugby World Cup to a recent Aerosmith concert.

800px-Otago_United_v_Waikato_FC_(1)

Natural grass surface on Indoor Forsyth Barr Stadium, Dunedin, NZ

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Aerosmith, recent performers on the grass of Forsyth Barr Stadium

So, the question from the interviewer to me essentially reduces to,  ‘Grass:  if its good enough for Steven Tyler and Joe Perry, is it good enough for all of us?’

Prior to the interview, I came across and read a wonderful piece from this very blog, written in 2011  by my predecessor and now CJSM Executive Editor Chris Hughes:  The Injury Risks of Artifical Turf in Soccer.   A focus of Chris’ piece is on a meta-analysis performed by Williams et al., “A Review of Football Injuries on Third and Fourth Generation Artificial Turfs Compared with Natural Turf.”  This study looked at injury rates of newer generation turf vs. grass playing surfaces across three football codes (soccer, rugby union, American football) and essentially found comparable rates of injury, with a slight increase in ankle injuries on turf.  The study group recommended that further study would be needed: “Clarification of effects of artificial surfaces on muscle and knee injuries are required given inconsistencies in incidence rate ratios depending on the football code, athlete, gender or match versus training.”

I commend Chris’ blog  piece to our readers as a complement to this blog entry posted two years later by an American clinician.

I stress the “American” adjective to note that the proverbial elephant in the living room in most of these discussions in American sports is American, gridiron football.  With my country’s idiosyncratic penchant for exceptionalism, we refer to the sport as ‘football,’ naming what I would guess six billion folks on this planet know as football as ‘soccer’.  In the discussions of turf vs. grass that occur in this country, the typical focus will be on the surface’s effect on American football.   This is not to say, of course, that the fields will not be used for a multitude of sports, including soccer, field hockey, softball, lacrosse; it is merely to note that in most of these multi-use venues, the ‘tail that wags the dog’ is the American football program and its needs or desires.

So, with that in mind, I set out to look at what evidence might exist in the medical literature that might be newer and complementary to what Chris found a couple of years ago, with a focus on epidemiologic studies focusing on injury rates in American football.  I found a couple of  interesting studies.

Dragoo et al. published an epidemiologic study in 2012 in The American Journal of Sports Medicine which concerned   the effect of turf on the incidence of ACL injuries in NCAA football.  The retrospective study looked at National Collegiate Athletic Asssociation (NCAA) Injury Surveillance data to calculate the association of ACL injury rates in American football players with various influencing factors (e.g. practice vs. competition, turf vs. grass, etc.)  The study authors found that there was a slight, but statistically signficant, increase in ACL injury rates on artificial playing surfaces compared with grass.  They calculated an injury rate of 1.73 ACL injuries per 10,000 athlete exposures (AEs) on turf as compared with 1.24 ACL injuries per 10,000 AEs on grass, a rate 1.39 times higher (95% C.I. 1.11 – 1.73).  They concluded, “The increased injury incidence on third-generation artificial turf may suggest that this surface is not an adequate substitute for natural grass….”  One strength of this study was its reliance on a well-established injury surveillance system.  The authors note several limitations, including, importantly, “…a large percentage of missing data, which may have ultimately skewed the results.”

bexley turf

Turf on local high school softball field, Ohio

The next study I looked at also was published in The American Journal of Sports Medicine: “Incidence, Mechanisms, and Severity of Game-Related College Football Injuries on FieldTurf Versus Natural Grass:  A 3-Year Prospective Study.” The study author, Michael Meyers, followed 24 Division IA NCAA football teams prospectively for three years and analyzed a total of 465 games (230 on FieldTurf and 235 on natural grass) over that period.  This study was exclusively looking at American football game play (as compared to, additionally, practices and scrimmages) and the specific newer-generation turf known as FieldTurf, described by Meyers as “…a polyethylene fiber blend stabilized with a graded silica and cryogenically ground rubber infill.”   The study looked at total injury rates and so-called ‘minor,’ substantial,’ and ‘severe’ injury rates on FieldTurf vs. grass:  ‘minor’ injuries were defined as those resulting in 0 to 6 days of time lost from sport, ‘substantial’ were those resulting in 7 to 21 days time lost, and ‘severe’ were those requiring 22 or more days out of sport.

Meyer used multivariate analyses to demonstrate significantly lower injury incidence rates on FieldTurf than on natural grass.  Rates were calculated as number of incidents per “10 team games.”   For instance, ‘severe’  injury rates on turf were found to occur 2.7 times per 10 games when compared with grass, where such incidents occurred 4.1 times per 10 games.  This finding was indeed statistically significant,  with = 0.049, a figure coming just under the defined a priori alpha value of 0.05.  Another way of looking at such data, which I typically find more instructive, is the 95% confidence interval (CI):  for severe injury rates on turf, the 95% CI was (2.1 – 3.3) and for grass the 95% CI was ( 3.5 – 4.1);  there was a difference, but it could literally be as small as 2 incidents per 100 games (for an American Division I NCAA football team that would be approximately 9 to 10 seasons).

That is, on the ‘lower end of effectiveness,’  FieldTurf may lower the number of  ‘severe’ injuries an American football team may see by a total of 2 over the course of 10 seasons (instead of 35 such injuries, ‘only’ 33).  That may or may not be ‘clinically significant,’ I would leave it for the reader to decide.

One of the strengths of this study was its prospective nature and the duration for which it was conducted, three years.  As far as limitations, the author notes several, including the possibility that injuries could have gone unreported or that there could be undefined confounders.  One dimension to which I am always particularly sensitive is the funding source for a study.  In this case, the research was funded by the product maker itself, FieldTurf.  My overall take on this study then is that it is intriguing, but the strength of the findings are not overwhelmingly substantial (i.e. its ‘clinical significance’ is unclear to me), and its chief weakness is that the study was funded by the product maker, something I would always rate a potentially significant limitation.

So, where do I stand on this issue?  I do have a bias, and it’s revealed in this photo of me running with my young son:

mo and me running

The grass between our toes….

I acknowledge that there may exist several factors schools or stadium officials may need to factor as they make their decisions regarding turf vs. grass.  There are issues of finance–the capital cost of installing turf, the on-going cost of grass maintenance, etc.–that are most definitely beyond my area of expertise.

However, from a point of view within my scope of expertise–athlete safety–I don’t yet see any solid evidence that turf can lower injury rates in athletes.  The aforementioned article in The Columbus Dispatch quotes me as saying  “If a (school) district asked him whether it should switch to fake turf, MacDonald said he would suggest holding off, at least until the data are more conclusive.”  I stand by that quote.

However, it is my hope that this blog will be a conversation and not a monologue.  I encourage all readers to participate in this conversation, and so please, share your thoughts and opinions, pro and con.  If you are aware of interesting studies in the medical literature that can inform this discussion, pass them on by all means.

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About sportingjim
I work at Nationwide Children's Hospital in Columbus, Ohio USA, where I am a specialist in pediatric sports medicine. My academic appointment as an Associate Professor of Pediatrics is through Ohio State University. I am a public health advocate for kids' health and safety. I am also the Emerging Media Editor for the Clinical Journal of Sport Medicine.

15 Responses to The Safety of Artificial Turf vs. Grass as a Sport Playing Surface

  1. Chris Hughes says:

    Hi all. One study I didn’t explicitly mention in my previous blog post on the injury risks of artificial turf in soccer was that by Ekstrand and colleagues published in BJSM ( see http://bjsportmed.com/content/40/12/975.full ) which was a prospective two-cohort study of male European elite football leagues comparing a heterogenous group with a control group of premier league players in Sweden. The authors found no evidence of a greater overall injury risk for players playing on artificial turf vs grass, apart from an increased incidence of ankle sprains on artificial turf which may have been artificially high due to the overall number of sprains being low. One limitation of this study was the fact that injury incidence in soccer seems to exhibit regional variation, so whether this had a direct influence on the results of this study or not is unclear.
    Injury risk is one thing, but regardless of this, for me the beautiful game is still best played on grass!

  2. sportingjim says:

    Our local school playing lacrosse on turf:

  3. Hello Everyone,

    First of all, thanks for writing a great article. I have experience playing in the Canadian Inter university Sport (CIS) Men’s soccer competition for 3 years on artificial turf as well as many years of experience playing on a natural surface. As a physiotherapy student and football fanatic I’m very interested in the the topic of artificial turf vs. grass and it’s effects on injury rates. In my personal experience there were far less injuries playing on artificial turf in Canada compared to playing on natural grass for the past few years in Australia. Of course there are many factors involved and I think that the poor condition of some of the Australian natural grass pitches we play on is a large factor. These are just personal observations. In terms of enjoyment I agree that you cannot beat a beautiful natural pitch!

    Cheers,

    Alex Mitchell

    • sportingjim says:

      Thanks for those comments they’re spot on.
      Aesthetics and personal bias aside, i completely agree
      with you: as ever in medicine, I think we need to look
      at the real data. It would be hard to decide against
      a particular surface if the evidence were such that it
      strongly demonstrated injury reduction one way or the other.
      Thanks again for reading and sharing in the conversation.

  4. Another article on this issue that you all may be interested in:

    “How artificial turf could change the future of soccer in North America.”

    http://m.mlssoccer.com/news/article/2013/05/02/how-artificial-turf-could-change-future-soccer-north-america-word

    • sportingjim says:

      That article looks great, we’ll check it out. Thanks for sharing.

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  6. sportingjim says:

    Enjoyed an MLS Soccer game at Columbus Crew Stadium (Montreal Impact vs. the Crew) played on Kentucky Bluegrass: https://twitter.com/CJSMonline/status/346308383659405313/photo/1

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  8. Nice comparison! Good article

  9. Noel says:

    Regarding injuries, a turf field is full of bacteria and a grazing (rug burn) on a turf field can be infected very easily. We usually carry antibacterial spray. A rug burn is not a serious injury (if not infected), however they are so frequent that they are annoying.

    A turf field is a heat mat. They play up to 35 degrees hotter than grass. Once again, an “injury” is hard to quantify in this regard. It is just unpleasant and detracts from the enjoyment of playing any sport in the outdoors.

    A plastic turf field does not absorb carbon dioxide or create oxygen. Grass is much more efficient at creating oxygen than trees, and definitely much better than plastic. This is slowly being eroded…and it’s a shame.

    As for playing on turf. I can only comment on Soccer.

    A younger team that does not have advanced skill sets, will tire quickly from never being able to get to the through ball.
    Spin on the ball is “over active” on a turf field and is as unpredictable as the “uneven bounce” from a grass field.

    Playing soccer on a pool table is as frustrating as playing pool on a clump of grass.

    Of course…these are only my opinions, however correct they may be.

    • sportingjim says:

      insightful comments, literature is coming out to support your opinions. i especially like the analogy you have made between soccer on a pool table/pool on a field of grass. thanks for writing.

  10. Alice says:

    It is important that studies to go into injury rates on artificial grass and way of changing this. Artificial grass is often a lot more practical for many schools and colleges so the more research into how we can help to keep the safer the better.

    • sportingjim says:

      agreed. there are many factors to consider, including the maintenance costs for school districts. thanks for your input!

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