Health impact

Chapter 9 of the Natural Grass vs Synthetic Turf Surfaces Study Final Report.

Synthetic turf has changed considerably since its inception in the 1960’s, however, concerns still exist around the potential negative health impacts of the surface. The perceived increase in injury risk on synthetic turf, compared to natural grass, has been debated for many years.  Recently, the potential harm from heat-related exposure and toxicity have become a major focus of attention. This section will present the current knowledge and evidence on the differences between natural grass and synthetic turf in terms of injury risk, and heat-related issues.

Injury risk

There has been a considerable lack of consensus on whether there is a higher risk of injury on natural grass or synthetic turf playing fields in the literature to date. This may be a consequence of inconsistencies in injury definitions, the lack of evaluating surface–related injuries only, or even the inherent variations between different synthetic products or different natural grass types. The surface properties of first and second generation synthetic turf were very different, in many respects, to the current third generation (3G) turf. The lack of impact absorption and the high friction/traction on the earlier surfaces were associated with an increased risk of injury.

In a review of the effects of synthetic turf and natural grass on surface –related injuries in soccer by Ekstrand & Nigg in 1989[1], they reported that there were more abrasion injuries sustained on the synthetic turf than the natural grass but no difference in the number of traumatic injury incidences between the two surfaces. Many subsequent studies, primarily in soccer and American football, reported an increase in injury risk on synthetic turf compared to natural grass.[2][3][4] While abrasions and lower extremity sprains were the most common injuries to have a higher rates on synthetic turf, an important study by Naunheim et al in 2002[5] examined the risk of head injuries between natural grass and synthetic turf. They found a difference in impact attenuation (i.e., the ability of the surface to absorb the force) between three surfaces; two indoor synthetic Astroturf (synthetic turf) and one outdoor natural grass playing surface. They suggested that a surface with low impact attenuation may contribute to a higher incidence of concussion injuries in American football players. 

Injury photos on natural grass 

Figure 1: Injury photos on natural grass.

The negative experiences and perceptions that ensued were to some extent responsible for the improvements to synthetic turf surfaces to replicate the characteristics of natural grass more closely.  It is notable that one study on first/second generation turf reported an increase in injuries on natural grass.[6] That particular study was an analysis of injuries in the National Football League (NFL) in the United States from 1989 to 1993 and showed that anterior cruciate ligament (ACL) injuries were five times more likely on natural grass than synthetic turf. This was an important finding as ACL injuries are both debilitating for the athlete and a high cost burden on the health care system. However, training injuries revealed the exact opposite result, with a higher risk of ACL injuries on the synthetic turf surface.48 Overall, injury rates appeared to be higher on first/second generations of synthetic turf compared to natural grass but despite all the research it remains uncertain whether footwear, environmental conditions or the surface itself was predominantly responsible.

Despite the fact that third generation or 3G turf playing fields began to appear in the late 1990s, the first study of injuries on these fields was not published until 2006. That study by Ekstrand et al (2006)[7] compared injuries on natural grass and 3G synthetic turf across 10 Swedish elite level male soccer clubs over three seasons and found no significant differences in injury rates and hence no greater risk on either surface. However, there was a higher incidence of ankle injuries on the 3G synthetic turf and a lower incidence of muscle strains. The authors acknowledged that the differences in injury patterns must be interpreted with caution as the numbers for specific injury subgroups were small. Notably, abrasion and friction burn injuries, which had been commonly reported on the previous generations of synthetic turf, were not identified as a problem in this study. However, the injury definition used by Ekstrand et al.49 only included those injuries that resulted in time loss from full training or matches and hence may have underestimated the abrasion type injuries.

Following this, Fuller et al (2007)[8] [9] compared injuries on natural grass and synthetic turf in the 2005 and 2006 American college soccer playing seasons, across genders and all games and training, and found no significant differences in the overall incidence, severity, nature or mechanism of injury. Although there was a significantly higher incidence of head/neck injuries in the male cohort on synthetic turf, none of those injuries were as a result of player-surface contact. The incidences of dermal injuries were also higher for the men on the synthetic turf and interestingly, the women recorded less ankle sprains on the synthetic turf. In training, the men had more incidences of ankle, foot and joint injuries and the women had less joint injuries on the synthetic turf. Similar results were reported in another study of 14-16 year old Norwegian female soccer players for the 2005 playing season. They also reported no significant difference in the overall risk of acute injuries between the surfaces but found a higher incidence of severe match injuries on the synthetic turf.[10]

Broken leg injury 

Figure 2: Broken leg injury

In the past 18 months, there has been a significant increase in the number of studies on injury risk on the latest 3G synthetic turf. Bjorneboe et al (2010)[11] published the first study on Federation Internationale de Football Association (FIFA) certified 3G synthetic turf. The significance of the certification is that the product would have undergone rigorous testing to satisfied a number of surface property standards before being played on.[12] These standards are based on durability and performance /safety and therefore the expectation is that the synthetic turf closely replicates natural grass. They studied the injuries of Norwegian male professional soccer players over four playing seasons and found no significant difference between injury location, type or severity between turf types for both training and match injuries. The injury definition used was time-loss based, i.e. an injury was registered if a player was unable to take part fully in soccer related activity for at least 1 day after the day of injury. Consequently, the study was limited to reporting acute injuries only.

In support of Bjorneboe et al’s work, a recent study published by Ekstrand et al (2010)[13] comparing the incidences and patterns of injury for female and male elite soccer players when playing on 3G turf and natural grass, found no differences in injury risk between the two surfaces. Their analysis of injury type revealed no significant differences but there were indications of a lower injury risk of quadriceps strains and a higher risk of ankle sprains on the synthetic turf during matches. Interestingly, they also indicated that men were more likely to sustain a calf strain on natural grass, but the number of injuries was small and therefore the differences didn’t reach a significant level. Similar to previous studies on 3G turf, they found a low number (0.4% of all injuries) of wounds, burns and friction injuries were sustained. This result is somewhat expected as the standards set by the governing bodies of the sports are demanding that the 3G surfaces satisfy friction standards before play. However, it is important to note that in their study they only included time-loss injuries and may have underestimated these types of injuries.

The results of a study undertaken over four consecutive Norway Cup tournaments,[14] which is a youth soccer tournament played over 6 consecutive days, comparing injuries on 3G synthetic turf compared to natural grass further supported the findings of Ekstrand et al55. They found that minor abrasions and friction burns associated with synthetic turf in early studies was not the case on 3G synthetic turf.56 The occurrence of abrasions and lacerations was low on both surfaces. A strength of this study was that it spanned 4 years and therefore included a wide range of conditions of the natural grass. Similar to all previous 3G studies, there was no difference in the overall risk of injury between the two surfaces.

In recognition of the limitations of previous studies to include chronic /overuse injuries Aoki et al (2010)[15] undertook a study comparing the incidence of injury, especially chronic injuries of adolescent soccer players, between natural grass and FIFA certified 3G synthetic turf. They monitored six teams of 12-17 year old males and again found no significant difference between the turf types but there was an association between chronic back pain and training on synthetic turf. However, they did postulate that it could be due to physical maturity or training hours as this differed between the natural grass and synthetic turf group. In light of this, they undertook further analysis and found that longer training hours on synthetic turf was a risk factor for younger, less mature adolescents. Although these results are interesting, the challenge with reporting and interpreting overuse injuries is controlling for confounding factors such as adaptation, event identification and other physical activity undertaken.[16]

In contrast to all other studies, there has been one recent study that found a greater incidence of injuries on natural grass compared to synthetic turf.[17] The synthetic turf product in their study was Fieldturf, which was specifically developed to replicate the playing characteristics of natural grass. They evaluated injuries from 2006 – 2008 in American college level football players and found more injuries on natural grass than synthetic turf (53.4% compared to 46.6%). They did not observe any differences in the category of injury between the surfaces or in head, knee or shoulder traumas. The factors that influenced the overall difference between the Fieldturf and natural grass were injury time loss, injury situation, grade of injury, injuries under various field conditions, and temperature.16 They suggested that the contrast in their results to previous studies were reflective of the advancements in synthetic materials.

As the use of synthetic turf is relatively new for rugby union, there has only been one study published to date comparing rugby union injuries on natural grass and 3G synthetic turf.[18] They found that there were no significant differences in the overall incidence or severity of injuries on synthetic turf compared to natural grass, although the incidence of minor injuries during training was significantly higher on synthetic turf. There was also a higher incidence (four times higher) of anterior cruciate ligament injuries during match play on synthetic turf but the sample size was too small to achieve a level of significance. It was also notable that in their study all concussion and skin lacerations were a result of player to player contact rather than player – surface contact. Although, the sample size in their study was small, the findings present some preliminary evidence to suggest that rugby union can continue to be played on synthetic turf but needs close monitoring as new products are evolving.60

A recent addition to the standards for synthetic turf has been the inclusion of a critical fall height in sports such as rugby union, Australian Rules football and Gaelic football. Critical fall height is an approximation of the height below which an individual may fall and most likely not sustain a severe head injury.[19] [20]

Since there is little published work to date on injuries on synthetic turf for these sports, the risk of head injuries from impacts has not been well established. A study by Theobald et al (2010)[21] on a variety of third generation soccer surfaces found that shockpads and infill were important in maximising the impact attenuation properties of the surface. Also they reported that moisture content did not influence the critical fall height and so safety remained consistent between arid and extremely wet conditions. They also found that impact attenuation of natural grass was dependent on its use and for players on poorly attended natural grass fields, the risk of a mild traumatic brain injury may be increased. Of the six 3G surfaces they tested, the fall heights ranged from 0.46 - 0.77 m for a 10% risk of sustaining a mild traumatic brain injury. With the increasing use of 3G synthetic turf for rugby union, and the impending use for Australian Rules football and Gaelic football, empirical evidence on the risk of head injuries on synthetic turf will hopefully be addressed in the near future.

A limitation of the work thus far is that it has focussed solely on the epidemiology of injuries or on the mechanistic nature of shoe-surface interactions but there is an immense need to develop an understanding of the underlying causes of injury on the different surfaces. As mentioned by Naunheim et al (2002)[22] in their work on head injuries on various surfaces, reporting the condition of the surface is critical to the correct interpretation of the results as the condition of all outdoor surfaces will vary according to environmental and maintenance conditions. A good description of the condition of the synthetic turf has not been included in most studies to date. An unmaintained field or moisture content could influence injury rates. Similarly, substandard natural grass fields or well worn areas on natural grass fields have been associated with a higher injury risk. Future studies investigating the mechanistic nature of injuries in the real-world context combined with details of the surface and footwear properties at the location of the injury will make a significant contribution to this area.

In summary, there were more injuries recorded on first and second generation synthetic turf compared to natural grass but currently there is insufficient evidence on third generation turf to draw the same conclusions. There appears to be a difference in injury patterns but not overall injury rates on third generation turf compared to natural grass. The multi-factorial nature of injuries makes it difficult to determine the exact contribution of the surface to the injury sustained. Future studies that include data on footwear, surface properties and detailed mechanistic information are undeniably needed.

Heat issues – natural grass and synthetic surfaces

In addition to an increased injury risk on synthetic turf, heat has become a factor of growing interest and concern. The lack of a natural cooling effect in synthetic turf compared to natural grass seems to have formed the basis for the unease. We know that the surface temperature increases with solar radiation load and is poorly related to air temperature[23] but to date the issue of the surface temperature of synthetic surfaces for outdoor sports has been poorly researched.[24]  Not only has the research been limited, but in some cases this potential problem has been ignored. Despite the increased use of synthetic turf, little thought has been given to the inherent qualities of the surface and the amount of heat radiated or reflected in Australian climatic conditions. Nonetheless, there is evidence to suggest that there is a difference between the effect of a synthetic surface versus natural grass on the heat load experienced by those exercising on outdoor grounds e.g., football, soccer, cricket.

Some early work on surface temperature on first /second generation synthetic turf identified increases in temperature on the synthetic compared to the natural grass, particularly when exposed to sunlight.[25] For example, a study by Buskirk et al. (1971)[26] reported differences in maximum temperature ranging from 35-60°C between the natural grass and synthetic turf. Similarly, Kandelin (1976)[27] found that over a 21 day period the maximum temperature reached by the natural grass was 45 degrees and 59 degrees by the synthetic turf. In general, heat-related research on the earlier generations of synthetic turf concluded that the physiological stress from the increased heat could be problematic.

Although there have been relatively few studies to date on 3G synthetic turf, the results have elicited the same findings. A study of heat on synthetic turf at Brigham Young University in the USA in 2009[28] reported temperatures as high as 93°C on the synthetic turf. They watered the synthetic turf in an attempt to reduce the temperature and found that the immediate effect was remarkable, a reduction from approximately 73.9°C to 29.4°C in the first few minutes. However, this effect was not sustained with the temperature rose to 73.3°C within twenty minutes. Watering has regularly been suggested to reduce the surface temperatures of the synthetic turf fields, but despite the fact that it is not always possible in drought-stricken regions, it is very temporary, unless large volumes of water are administered.[29]

Another study that examined the differences between a synthetic outdoor futsal field and a natural grass field in Japan reported a difference of 16.4 degrees between the surfaces in September but that difference was reduced to 4.5 degrees in December.[30] These results highlight the effect of direct sunlight compared to days of cloud cover. Data was also published on the differences between natural grass, synthetic turf, tennis courts and a running track.[31] The results have been summarised in Table 8 below and demonstrate that the temperatures on natural grass are lower than the other surfaces. 

Table 1: A synthesis of surface and air temperature results of three studies on surface termperatures of different outdoor surfaces

Study

Air temperature

Natural grass

Green synthetic turf

White synthetic turf

Soil

Asphalt

Artificial track

Clay track

Artificial turf tennis

Williams& Pulley (2009)#

27.5

25.7

47.2

 

36.8

43.1

 

 

 

Aoki (2005)

11am summer

42.2

67

 

 

 

63.9

45.1

59.3

Aoki (2005)

11am winter

11.5

19.6

 

 

 

21.8

10.8

11.8

Devitt et al (2007)

44.5max

38*

76

66.4

59*

60.9

 

 

 

# These data were reported as average temperatures for a period between 7am and 7pm and the temperatures have been converted from Fahrenheit to Celsius.  * estimated from graph as exact temperature was not reported.

During the development of guidelines for synthetic turf for Australian Rules football and cricket, some pilot data was collected on the temperatures on a synthetic turf field in Australia.[32]  Despite the limited data, it provides some indication of the temperatures that can be expected in the Australian climate refer to Table 2 .

Table 2: A summary of all field testing sites and temperatures recorded at each site (adapted

Ground type

Weather

Air temp (0C)

Surface temp(0C)

RatioSurface - Air

Grass

Sunny

28.7

39.6

1.38

Grass

Sunny

25.0

36.1

1.44

Grass

Overcast

16.4

16.8

1.02

Synthetic

Sunny

26.6

34.5

1.3

Synthetic

Sunny

38.6

63

1.63

Synthetic

Overcast

20.9

22.2

1.06

Synthetic

Sunny (3pm)No wind

42.1

72.7

1.73

Synthetic Sunny (4.30pm) Windy 58.6 1.65

Synthetic

Sunny 54.7(Max-63) 1.81

Table 2: A summary of all field testing sites and temperatures recorded at each site (adapted with permission from Twomey et al29).

The information above shows that on all occasions, the surface temperature of synthetic turf was greater than natural grass. The effect of these temperature differences on sports participants is unknown and untested in Australian conditions. Currently guidelines for safe exercising in the heat have been developed by Sports Medicine Australia. This peak organisation have produced three resources which cover hot weather guidelines and tips for preventing heat related illnesses and strategies for sporting organisations and these can be found at the following address: http://sma.org.au/resources/policies/hot-weather/. They provide general guidelines and deal only with ambient temperatures and relative humidity and are not related to surface temperatures of the grounds. It is known that children and adolescents do not adapt as well to heat stress as an adult when exercising and therefore are more vulnerable to heat illnesses and extra precautions need to be taken.

In conclusion, the evidence to date suggests that there is an increase in peak temperatures on 3G synthetic turf. The composition of the 3G turf makes it difficult to ascertain what component(s) of the product are responsible for the increased temperatures. In addition, factors such as wind, humidity and cloud cover may all contribute to the surface temperature and have not yet been tested simultaneously. Recently, there has been a move in the synthetic turf industry to produce ‘heat-resistant’ products but currently they have not been sufficiently tested in the natural environment to compare them to natural grass. Future research is needed to quantify temperatures on the latest products and where necessary develop heat safety policies for synthetic turf on surface temperatures and not solely based on air temperatures. 

Footnotes 

  1. Ekstrand J, Nigg B. Surface-related injuries in soccer. Sports Medicine 1989;8:56-62.
  2. Arnason A, Gudmundsson A, Dahl H. Soccer injuries in Iceland. Scandinavian Journal of Medicine & Science in Sport 1996;6:40-45.
  3. Stanitski CL, McMaster JH, Ferguson RJ. Synthetic turf and grass: A comparative study. Am J Sports Med 1974;2(1):22-26.
  4. Engebretsen L. Fotballskader og kunstgress. Tidsskrift for den Norske lægeforening 1987;107(26):2215.
  5. Naunheim R, McGurren M, Standeven J, Fucetola R, Lauryssen C, Deibert E. Does the use of artificial turf contribute to head injuries? The Journal of Trauma: Injury, Infection, and Critical Care 2002;53(4):691 - 693
  6. Scranton PE, Whitesel JP, Powell JW, Dormer SG, Heidt RJ, Losse G, et al. A review of selected noncontact anterior cruciate ligament injuries in the National Football League. Foot  & Ankle International 1997;18(12):772 - 776.
  7. Ekstrand J, Timpka T, Hagglund M. Risk of injury in elite football played on artificial turf versus natural grass: a prospective two-cohort study British Journal of Sports Medicine 2006;40(12):975-980.
  8. Fuller CW, Dick RW, Corlette J, Schmalz R. Comparison of the incidence, nature and cause of injuries sustained on grass and new generation artificial turf by male and female football players. Part 2: training injuries. British Journal of Sports Medicine 2007;41(suppl_1):i27-32.
  9. Fuller CW, Dick RW, Corlette J, Schmalz R. Comparison of the incidence, nature and cause of injuries sustained on grass and new generation artificial turf by male and female football players. Part 1: match injuries. British Journal of Sports Medicine 2007;41(suppl_1):i20-26.
  10. Steffen K, Andersen TE, Bahr R. Risk of injury on artificial turf and natural grass in young female football players. British Journal of Sports Medicine 2007;41(suppl_1):i33-37.
  11. Bjorneboe J, Bahr R, Andersen T. Risk of injury on third generation artificial turf in Norwegian professional football. British Journal of Sports Medicine 2010;44:794-798.
  12. Federation Internationale de Football Association (FIFA). FIFA Quality Concepts for Football Turf: Handbook of requirements. May 2009 ed, 2009.
  13. Ekstrand J, Hagglund M, Fuller C. Comparison of injuries sustained on artificial turf and grass by male and female elite football players. Scandinavian Journal of Medicine & Science in Sport 2010; In press.
  14. Soligard T, Bahr R, Andersen T. Injury risk on artificial turf and grass in youth tournament football. Scandinavian Journal of Medicine & Science in Sport 2010:1-6.
  15. Aoki H, Kohno T, Fujiya H, kato H, Yatabe K, Morikawa T, et al. Incidence of injury among adolescent soccer players: a comparative study of artificial and natural grass. Clinical Journal of Sports Medicine 2010;20(1):1-7.
  16. Bjorneboe J, Bahr R, Andersen T. Risk of injury on third generation artificial turf in Norwegian professional football. British Journal of Sports Medicine 2010;44:794-798.
  17. Meyers M. Incidence, mechanisms, and severity of game-related college football injuries on FieldTurf versus natural turf: A three year prospective study. American Journal of Sports Medicine 2010;38(4):687-697.
  18. Fuller C, Clarke l, Molloy M. Risk of injury associated with rugby union played on artificial turf. Journal of Sport Sciences 2010;28(5):563-570.
  19. Laforest S, Robitaille Y, Lesage D, Dorval D. Surface characteristics, equipment height, and the occurrence and severity of playground injuries. Injury Prevention 2001;7(1):35-40.
  20. Twomey D, Otago L, Saunders N. The effects of testing procedure on critical fall height determination for third-generation synthetic turf. Sports Engineering 2011;13(3):145-151.
  21. Theobald P, Whitelegg L, Nokes L, Jones M. The predicted risk of head injury from fall related impacts on to third-generation artificial turf and grass soccer surfaces: a comparative biomechanical analysis. Sports Biomechanics 2010;9(1):29-37.
  22. Naunheim R, McGurren M, Standeven J, Fucetola R, Lauryssen C, Deibert E. Does the use of artificial turf contribute to head injuries? The Journal of Trauma: Injury, Infection, and Critical Care 2002;53(4):691 - 693.
  23. Devitt D, Young M, Bird  B, Baghzouz M. Surface temperature, heat loading and spectral reflectance of artificial turfgrass. Journal of Turfgrass and Sports Surface Science 2007;83:68-82.
  24. Aoki T. Current state and perspective for artificial turf as sport environment ・ Focusing on Third-generation Artificial Turf as Football Playing Surface. Retrieved from http://libir-bw.bss.ac.jp/jspui/handle/10693/161 June 27, 2011, 2005.
  25. McNitt AS. Synthetic turf in the USA - Trends and issues. International Turfgrass Society 2005;10:27-33.
  26. Buskirk ER, Loomis JL, McLaughlin ER. Microclimate over artificial turf. Journal of Health, Physical Education, and Recreation 1971;42(9):29-30.
  27. Kandelin W, Krahenbuhl G, Schacht G, Schacht C. Athletic field microclimates and heat stress. Journal of Safety Research 1976;8:106-111.
  28. Williams C, Pulley G. Surface Heat Studies, Brigham Young University. http:aces.nmsu.edu/programs/turf/documents/brigham-young-study.pdf, 2009.
  29. Williams C, Pulley G. Surface Heat Studies, Brigham Young University. http:aces.nmsu.edu/programs/turf/documents/brigham-young-study.pdf, 2009.
  30. Aoki T, Matsuda T, Toyoda K. Sport environments for children-Focusing on surface layer temperature of artificial turf. Bulletin of Biwako Seikei Sport College 2005;2:93-98.
  31. Aoki T. Outdoor sports surfaces made from organic polymer were hot. Training Journal 2005;312:38-39.
  32. Twomey D, Otago L, Saunders N, Schwarz E. Development of standards for the use of artificial turf for Australian football and cricket. Ballarat: University of Ballarat, 2008.