Magazine: Performance of Turfgrass Playing Surfaces and Sporting Injuries
By Simon Kars in Consultancy on 13th Mar 2008 6:00
Performance of Turfgrass Playing Surfaces and Sporting Injuries 
Simon has completed his degree in Horticulture & Turf Management at Melbourne University; Simon devotes his work between golf courses & stadium management. Simon is currently gathering tournament experience on golf courses.
Introduction
Australian Rules Football (AFL) accounts for one third of sporting injuries. The injury costs to the AFL are significant and many varying research projects have been authorised by the AFL to reduce injury costs and increase the safety of the game. Sports injuries cost Australia approximately $1.65 billion a year. Injuries in the AFL still result in 15% of the listed players being unable to play at any time, despite the best efforts to prevent injury. With the continuing increase in popularity of professional football and greater expectations made on players, stronger demands are being placed on the playing quality of the grassed surface.
Recent studies have revealed a relationship between non-contact Anterior Cruciate Ligament (ACL) injuries, and various factors that create traction between the sportsman and the turfgrass playing surface. Many authors have concluded that greater rotational traction rather than hardness of a turfgrass playing surface, could result in a greater risk of ACL injurie
s among sports players. Factors such as species type, surface hardness, thatching and cleat design influence the amount of traction within a turfgrass playing surface. Various machines have been created to measure traction within a turfgrass playing surface, but a device that best imitates the contact of a sportsman’s foot and the playing surface, will provide the most significant measurement of traction.
The Injury
The Anterior Cruciate Ligament (ACL) is the primary stabilizer ligament of the knee. It is a strong fibrous band about the size of your little finger, similar to a cable. Ligaments are strong bands of tissue that connect one bone to another. The ACL is in the centre of the knee joint, and connects the thigh bone (femur) to the shin bone (tibia).
The ACL connects and stabilizes the two main bones of the knee joint, and it limits the twisting and forward sliding motion of the knee (University Sports Medicine, n/a). As current ankle strapping is very strong, the ankle will not give way and the next weakest point (the knee ligaments) could tear and cause damage. It is typically torn when the knee twists abnormally, or is in a collision or accident. Often, a snap or pop is felt as the knee gives out, and is followed by immediate pain and swelling (University Sports Medicine, n/a). Almost always, a return to activity is not possible, making the injury a career ending one among professional sportsman.
When the ACL is torn from abnormal twisting of the knee, this is what is referred to as a non-contact ACL injury. The various extrinsic risk factors that influence this abnormal twisting of the knee on a turfgrass playing surface, is what is measured and analyzed to determine what is a safe playing surface for the professional sportsman.
Significance of grass type and risk of player injury
From various studies, it has been concluded that the grass type plays a vital role in the link between the turfgrass playing surface and the potential risk of non-contact ACL injuries. In recent trails conducted by Aldous and Chivers (2003), the occurrence of grasses that have large amounts of above ground stems seems to be closely matched to that of ACL injury rates. It has been suggested that such grasses could, in effect “trap” a player’s boot and prevent it from freely rotating within the turf. Thus the player, in attempting to revolve his foot in order to turn himself, will find his foot trapped and unable to revolve (Aldous and Chivers, 2004), resulting in the abnormal twisting of the knee.
Grass types are comprised into two main categories, warm-season and cool-season grasses. Such
cool-season grasses that are used within a turfgrass playing surface can be, Poa annua (winter grass) and Lolium perenne (perennial rye grass), and a warm-season grass, which is used within a turfgrass playing surface, called Cynodon dactylon (couch grass). The study by Aldous and Chivers (2003) measured the amount of Cynodon dactylon and Poa annua within the non-Melbourne and Melbourne AFL grounds. The results gave a strong indication that the factor most likely to be contributing to the higher incidence of ACL injuries on non-Melbourne grounds, is the percentage of Cynodon dactylon in the turfgrass surface. Cynodon dactylon is a warm-season growing perennial turfgrass that spreads by stoloniferous growth, and is known for its aggressive growth over summer. Cynodon dactylon dominates many of the non-Melbourne grounds especially at the start of the season, prior to oversowing, which is the technique of sowing grass seeds into an existing pasture without preparing a traditional, ploughed and cultivated seedbed of the surface (Aldous and Chivers, 2003). When the content of Cynodon dactylon is added together with the content of Poa annua in the turfgrass, (both tend to have large amounts of aboveground stems and stollens), the result is even more closely matched to that of ACL injury rates.
Orchard (2005) suggests that Lolium perenne is associated with fewer non-contact anterior cruciate ligament injuries, than Cynodon dactylon (or its hybrid species). The objectives of the study is to assess the contribution of ground variables including grass type to the risk of ACL injury in the AFL, specifically which factors are primary responsible for previously observed warm-season grass type, and early season biases for ACL injuries. Orchard (2005) then states rye grass appears to offer protection against ACL injury compared with Bermuda (couch) grass fields. The likely mechanism is reduced “trapping” of the football boots by less thatch. Grass species as a single consideration cannot fully explain the ACL early season bias, but is probably responsible for the warm-season grass type bias seen in the AFL.
Significance of Thatch and risk of player injury
Thatch in turf is defined as a layer of dead and living shoots, stems and roots that develop on the
surface of a root zone bellow the green tops. Moderate amounts of thatch on grassed sports grounds are likely to be slippery, dry out more frequently, and are more prone to become compacted. Excessive thatch can minimize the movement of air fertilizers into the soil layer that weaken the turf, create localized dry spots, render certain pesticides ineffective, and trap player’s boots, all factors that increase the potential for player injury. Aldous and Chivers (2003) concluded that thatch depth depends on the grass type, and the composition of the grass type used within a turfgrass playing surface.
Significance of hardness and risk of player injury
Surface hardness has been defined as the ratio of an applied force to the amount of surface deformation (i.e. stiffness) (Bell et al., 1985), or “the ability of the surface to absorb shock imparted by the colliding object” (Puhulla et al. 1999). The term hardness is often used to cover the player surface conditions that relate to running andfalling. Baker and Canaway have found that surface hardness decreases as soil moisture content increases, and can influence the condition of the turfgrass surface layer. One of the machines used to measure surface hardness is the Clegg Impact Hammar®. The machine can gauge the shock absorption potential in the turf surface, to determine the possible harm to AFL players when making contact with the ground (Aldous and Chivers, 2004). Orchard (2001), concluded that there was a non-significant trend towards more ACL injuries on harder grounds, and that surface hardness (independent of shoe-surface traction), is unlikely to be the most important extrinsic factor for ACL injuries across a variety of spots. Orchard (2001) used the Penetrometer instrument on each of the AFL turfgrass playing surfaces, to measure surface hardness in sports fields.
Cleat Design
Lambson (1996) evaluated torsional resistance of modern football cleat designs, and the incidence of surgically documented anterior cruciate ligament tears in high school football players wearing different cleat types. Lambson (1996) stated that traction is a critical component for efficient performance in most athletic events, and is closely related to the design characteristics of the sport shoe. Different cleat designs will cause a greater traction within a turfgrass playing surface. But it’s often the case that AFL players desire greater traction on a playing surface to increase their skill level, using a high traction cleat design boot. But of particular concern was the introduction of a cleat design, which included longer cleats around the exterior of the sole, as well as smaller cleats on the interior portion. This type of design enhanced traction and was commonly worn by athletes who sustained serious knee injuries. Lambson also used a Vermont Release Calibrator Device, similar to that of the Pennfoot® Device (McNitt et al., 1997), which measured the traction of various boot cleat designs. From the study Lambson (1996) recommended the non-edge cleat designs for athletes to prevent major knee injuries.
Traction
Traction comes in different forms depending on the particular forces evolved in each case. Linear traction refers to the resistance to a shoe sliding across a surface. Rotational traction refers to the traction that resists rotation of the shoe during pivoting movements. Therefore, being able to take accurate and meaningful measurement of rotational traction is most important, in terms of minimizing the risk of knee and ankle injuries to players with studded shoes. Static and dynamic traction represents slightly different aspects of the shoe-surface interaction. The static part of traction is the forces resisting the initiation of the shoe pivoting or sliding. Dynamic traction is the resistant forces that occur during the sliding and pivoting of a shoe. Therefore rotational traction, is the form of traction that is the main contributing force that causes ACL injuries to AFL players.
Various types of devices measure rotational traction within turfgrass playing surfaces and/or artificial surfaces. One such device is the studded disc apparatus, which was developed by Canaway (1975) and further developed by Canaway and Bell (1986). The main component is a horizontal disc with football studs fitted equidistant from the vertical shaft. The disc, which weights at least 40 kilograms is dropped manually onto the playing surface to ensure penetration and then rotated to tear the turf, measuring the amount of rotational traction in Newton meters (Nm) with a torque wrench. The development of the Pennfoot® by McNitt (1997), displayed a notable advancement in traction measurement since the mid-1980s. The hydraulically-operated Pennfoot consists of a framework supporting a leg and foot assembly, that can be used to measure both rotational and linear traction using different footwear under various loading weights. The Queensland Department of Primary Industries and Fisheries developed the Automated Turf Tester, which incorporated some new ideas into the studded disc apparatus. This device is able to create a profile of torque, with respect to the angular displacement of the rotatable shaft, to define accurately the characteristics of the surface under test. The device that best simulates the interaction of a sportsman’s foot in contact with the playing surface will provide the most meaningful measurement of rotational traction.
The objectives of this study is to create a set of standards for turfgrass managers, which rate the performance of the turfgrass playing surface based on the amount of traction created within the playing surface. From these standards, a turfgrass playing surface can be maintained, which is desirable for both the players and the spectators of the sport.
Calibration of the equipment used and testing for direct application, will determine the accuracy and validity of the results obtained in this study.
References
Aldous D.E., I.H. Chivers and Kerr R., 2005, Player perceptions of Australian Football league grass surfaces, International Turfgrass Society Research Journal, Vol. 10, pp. 318-326.
Baker S.W., 1999a, Temporal variation of selected mechanical properties of natural football pitches, J. Sports Turf Res. Inst., Vol 67: 83-92.
Orchard J.W., Chivers I., Aldous D., Bennell K. and Seward H., 2005, Rye grass is associated with fewer non-contact anterior cruciate ligament injuries than Bermuda grass, British Journal of Sports Medicine, 39:704-709.
Orchard J. and Seward H., 2001, AFL Injury Report.
Roche, 2003, Putting science behind traction measurement, Australian Turfgrass Management Magazine.
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Performance of Turfgrass Playing Surfaces and Sporting Injuries 
s among sports players. Factors such as species type, surface hardness, thatching and cleat design influence the amount of traction within a turfgrass playing surface. Various machines have been created to measure traction within a turfgrass playing surface, but a device that best imitates the contact of a sportsman’s foot and the playing surface, will provide the most significant measurement of traction.
cool-season grasses that are used within a turfgrass playing surface can be, Poa annua (winter grass) and Lolium perenne (perennial rye grass), and a warm-season grass, which is used within a turfgrass playing surface, called Cynodon dactylon (couch grass). The study by Aldous and Chivers (2003) measured the amount of Cynodon dactylon and Poa annua within the non-Melbourne and Melbourne AFL grounds. The results gave a strong indication that the factor most likely to be contributing to the higher incidence of ACL injuries on non-Melbourne grounds, is the percentage of Cynodon dactylon in the turfgrass surface. Cynodon dactylon is a warm-season growing perennial turfgrass that spreads by stoloniferous growth, and is known for its aggressive growth over summer. Cynodon dactylon dominates many of the non-Melbourne grounds especially at the start of the season, prior to oversowing, which is the technique of sowing grass seeds into an existing pasture without preparing a traditional, ploughed and cultivated seedbed of the surface (Aldous and Chivers, 2003). When the content of Cynodon dactylon is added together with the content of Poa annua in the turfgrass, (both tend to have large amounts of aboveground stems and stollens), the result is even more closely matched to that of ACL injury rates.
surface of a root zone bellow the green tops. Moderate amounts of thatch on grassed sports grounds are likely to be slippery, dry out more frequently, and are more prone to become compacted. Excessive thatch can minimize the movement of air fertilizers into the soil layer that weaken the turf, create localized dry spots, render certain pesticides ineffective, and trap player’s boots, all factors that increase the potential for player injury. Aldous and Chivers (2003) concluded that thatch depth depends on the grass type, and the composition of the grass type used within a turfgrass playing surface.
