Andrew S. McNitt, The Pennsylvania State University
Dianne Petrunak, The Pennsylvania State University
Numerous studies have been conducted to evaluate the safety and playability of traditional (non-infill) synthetic turf surfaces. Three methodologies are used to compare the safety and performance of various surfaces. These include 1) material tests where mechanical devices simulate human movement and measure the associated forces; 2) human performance tests where researchers measure the forces associated with the interaction of a human subject and a surface; and 3) epidemiological studies in which the number and type of injuries sustained by athletes during actual sporting events are counted.
Material tests have been completed that measure the shoe-surface traction and surface hardness of synthetic turf surfaces (Bowers and Martin, 1975; McNitt and Petrunak, 2001; Valiant, 1990). Human subject tests have shown improved athlete performance on traditional synthetic turf when compared to natural turfgrass (Krahenbuhl, 1974; Morehouse and Morrison, 1975) and epidemiological studies have counted the number of knee and ankle injuries on synthetic versus natural turfgrass (Meyers and Barnhill, 2004; Powell and Schootman, 1992; Powell and Schootman, 1993).
No large-scale epidemiological studies have been published comparing the number of surface-related injures sustained by athletes playing on infill synthetic turf systems to the number of injures sustained on either traditional synthetic turf or natural turfgrass surfaces. One study (Meyers and Barnhill, 2004) compared injury incidence of eight high school (American) football teams in Texas USA playing on infilled synthetic surfaces (FieldTurf) and natural turfgrass surfaces. Although similarities in injury occurrence existed between FieldTurf and natural grass fields over a five-year period of competitive play, there were significant differences in injury time loss, injury mechanism, anatomical location of injury, and type of tissue injured between playing surfaces. The researchers reported higher incidences of 0-day time loss injuries, noncontact injuries, surface/epidermal injuries, muscle-related trauma, and injuries during higher temperatures on FieldTurf compared to natural turfgrass surfaces. Higher incidences of 1- to 2-day time loss injuries, 22+ day time loss injuries, head and neural trauma, and ligament injuries were recorded on natural turfgrass fields compared to FieldTurf. The researchers state a number of limitations to their study including the random variation in injury typically observed in high-collision team sports and the percentage of influence from risk factors, other than simply surface type. Field conditions at the time of injury were not measured although the researchers noted that the majority of injuries (84.4%) occurred on natural turfgrass surfaces under conditions of no precipitation (dry surface).
The United States National Collegiate Athletic Association (NCAA) is collecting injury data from numerous men's and women's sporting events across the United States using a computerized system called " NCAA Injury Surveillance System" (National Collegiate Athletic Association, 2004) but presently does not have sufficient data from which to draw conclusions (R. Dick, 2004, personal communication).
Stefanyshyn et al. (2002) used human performance comparisons to evaluate 20 configurations of infill synthetic turf systems. Human subjects performed various maneuvers on the surfaces and the forces associated with the cleated foot interacting with the surface were recorded in the laboratory using a force plate installed beneath the turf surface. Stefanyshyn et al. (2002) reported a significant range of traction and surface hardness differences among the infill synthetic surfaces (Table 1) and grouped the 20 infill surfaces into categories of highly recommended, recommended, and not recommended based on surface hardness and both the rotational and translational (linear) traction recorded on these surfaces.
Shorten et al. (2003) performed material tests in which weighted shoes were dragged across varying infill synthetic turf systems and traditional synthetic turf. The translational and rotational traction of the various shoe-surface combinations were measured. The researchers concluded that both shoes and surfaces significantly affect traction. On all surfaces tested, shoes with lower profile cleats or studs had better overall traction performance compared to shoes with longer cleats and infill systems had better traction performance than traditional synthetic turf. Traction performance was calculated using an index where rotational traction values were subtracted from translational traction values. To eliminate scaling and range differences between the translational and rotational resistance measures, calculations were done using "standard scores" rather than raw data. The standard score is a measure of where a particular result lies relative to the average and distribution of all the results recorded: ex. Standard Score = (Actual Score − Average Score) / (Standard Deviation of All Scores). The researchers stated that further research is required to determine the effects of moisture, temperature and aging on surface traction performance. Both the study by Stefanyshyn et al. (2002) and the study by Shorten et al. (2003) were performed on newly constructed infill systems in a laboratory setting.
