Monday, June 17, 2013

Injury Risk: Artificial Turf vs Natural Grass

Years ago, many players, coaches and trainer felt that playing or training on artificial turf lead to more injuries. This was true for soccer as well as other sports like American football, field hockey and lacrosse. Recent advances in technology have lead to “third generation” artificial turf that can be found on many public fields and in some professional stadia. But, the debate continues. Does playing or training on turf raise injury risk? Over the past several years, several studies have compared injury rates on turf and grass for several sports. Recently, we compiled the research on soccer and, using a meta-analysis attempted to determine if there is increase risk of injury on turf. We found that playing or training on turf does not raise the potential for acute injury. However, changes in the style of play and/or player perception of turf may affect injury risk.


A meta-analysis is a technique where the results of several research studies are statistically combined to obtain a consensus result. One advantage of this approach is that much more data are used in the analysis than could be included in a single study. Also, a meta-analysis includes studies conducted by several different researchers at multiple locations and using different athletes. Thus, it amounts to a “big picture” look at the problem emerges from this type of analysis.

We reviewed a number of individual studies of injuries occurring on artificial turf and natural grass. Of these, eight were selected for the final analysis. These eight were consistent in that they 1) monitored players training or matches played on both turf and grass, 2) they reported the number of injuries and the number of hours spent training and playing (exposure time), and 3) were consistent in how they determined an injury (an “injury” required the player to miss at least one day of training or match play). We then extracted the raw data (number of injuries and exposure time) as well as the characteristics of the players.

In total, the eight studies resulted in nearly 1.5 million hours of play (exposure time) and almost 10,000 injuries. Slightly less than two-thirds of the exposure time was spent on grass while more that 75% of the injuries occurred on grass. When we combined all injuries across both matches and training, we found that the risk of injury on turf was 10-14% lower that on grass. This was the case for males and females as well as youth and adults. As for specific injuries, there was a lower risk of knee, ankle and foot injuries on turf. The risk of muscle strains was similar for both surfaces.

Our results argue against the idea that playing or training on artificial turf increases the risk of injury. In fact, turf may actually reduce the risk of some specific injuries under specific conditions (more about this later).

How do we explain the results? Studies show that artificial turf has some key characteristics that may reduce the stress placed on joints. This is certainly the case when turf is compared to a low-quality grass field that may be dry, hard and marked with ruts and bare spots. However, there is no consensus on this idea and the studies we examined all reported high-quality grass fields. Another key issue is that the game changes when played on turf. Ball speed increases and movement patterns change. Players also tend to adopt a less aggressive style of defending (e.g. fewer slide tackles). This could affect the number of injuries suffered, regardless of the playing surface. Lastly, players generally have negative perceptions about playing on turf. They often feel more fatigued after playing on turf and see the need for greater technical skills. This could be due to the increased speed of the game or to playing on a “softer” surface. At this time, we’re not sure of their perceptions are correct, but the reality is that the perception of fatigue and game speed can alter the how a player approaches the match. So, there are several reasons why injury rates may differ between turf and grass surfaces. And these reasons may be indirectly tied to the field surface.

What have we missed? First is heat. None of the studies reported heat-related injuries. There is little argument that heat can be a major factor when playing on turf. Surface temperatures on a hot day can reach well over 100 degrees F (38 degrees C). Second, abrasion injuries are usually not counted in these studies. To be classified as an “injury”, a player must have missed one or more days of training or match play. Few players miss much (if any) time due to an abrasion suffered during a slide tackle. Given the abrasive nature of turf, one would assume that more abrasions occur on that surface compared to grass. However, at this time, we don’t have any research to back that up. Third, the research in this area is lacking in some respects. More information is needed on females and youth players. Given that more and more local facilities are installing turf fields that are used by youth teams, it’s important to understand how turf may or may not affect injury rates in this group of players. Also, more information is needed on chronic injuries. These are not included in the studies because it is difficult to tie a chronic injury to one surface or the other.

Our study indicates that playing matches or training on artificial turf does not increase the risk of players suffering an injury. In fact, the risk of some injuries, under some conditions is actually reduced when playing on turf. However, at this point, we’re not willing to go so far as to say artificial turf is safer than grass. Clearly more work needs to be done, particularly understanding players’ negative feelings about turf and the possibility that the amount of energy expended when playing and training on turf is greater compared to grass. The bottom line? Based on current research, players, coaches and parents should feel comfortable about soccer played on artificial turf. The likelihood of suffering an acute injury because of artificial turf is no greater than when playing on grass.

Reference

Williams JH, Akogyrem M, Williams, JR (2013) A meta-analysis of soccer injuries on artificial turf and natural grass. Journal of Sports Medicine, Article ID 380523, 6 pages.

Many thanks to Emmanuel Akogyrem and Jeremy Williams for their work on this project.