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Testing Synthetic Turf Surfaces

By Arthur Eddy, ASLA, LEED AP

As we approach the fall season, athletics is gearing up for the long fall season, so this is a good time to start to discuss testing synthetic turf surfaces. Testing gives a field manager an understanding of how the surface is performing and what maintenance procedures should take place to ensure a field is performing and safe. Both safety and performance are equally important and should be part of an annual routine. In this article we will focus on some safety tests that will help to limit the exposure of a facility and keep athletes safe:

GMax: The most common field test on a synthetic surface is GMax. GMax is the measurement of the hardness of the surface or the impact an athlete’s head will have with the surface. The harder the surface or the higher the GMax, the more critical the impact can be on the athlete. The softer the surface or the lower the GMax can reduce the impact. Reducing the GMax can reduce a player’s probability of a head injury, but care should be given to not make a field too soft which will impact other tests outlined below. GMax of a natural grass field is typically 75-115 G’s. The NFL has instilled a concussion protocol limit for critical injury of 165 G’s and the American Society of Testing Materials (ASTM) F1936-19 has a limit of 200 G’s.

Rotational Resistance Testing

Photo credit: Sportlab USA

Head Injury Criteria (HIC): Similar to GMax, Head Injury Criteria is an effective way to measure the probability of a head injury to a player. The difference between GMax and HIC is the means in which the test is conducted. A spherical apparatus is dropped on the surface that mimics the form of a human head. Measurements are based on critical fall heights that measure hardness and softness of the surface and at which height there would be a critical injury to the athlete. The World Rugby association has a critical fall height of greater than 1.34 meters.

Ball Drop Testing

Photo credit: Sportlab USA

Vertical Deformation: Vertical deformation is the measurement of how much the surface is moving under foot. The easiest comparison is the idea of running in sand. A surface that deforms too much or too soft, will result in overstretching of ligaments particularly around the ankle and can potentially cause damage to player’s joints based on the surface energy resulting in the higher probability of fatigue and overuse injuries. Surfaces that are too hard can lead to discomfort in the feet or injuries such as shin splints. Vertical deformation is measured in millimeters and FIFA has a range of 4mm-10mm.

Rotational Resistance: Rotational resistance simulates a player’s ability to alter direction.Too high of a value and stress can occur across knee ligaments; too low and the player will not be able to grip the surface and may slip causing ligament damage. Rotational resistance is measured in N/mm and FIFA has a range of 30Nm-50Nm. As groundskeepers, the safety of athletes and users on our synthetic surface is a critical component of our responsibility. Each of these tests are dramatically impacted by the level of maintenance of the surface. Assuming the field passed the outlined tests at installation, a field that is well maintained will be able to continue to meet the criteria outlined above and provide enjoyment for all its users. Getting the surface tested on an annual basis is a small cost compared to the potential exposure to liability that an unmaintained facility can create.

Ball Roll Testing

Photo credit: Sportlab USA

REFERENCES:

https://football-technology.fifa.com/en/media-tiles/fifa-qualityprogramme-for-football-turf-1/

https://www.syntheticturfcouncil.org/page/OneTurf

https://www.world.rugby/the-game/player-welfare/surfaces/one-turf

https://www.astm.org/Standards/F1936.htm

Art Eddy is CEO of RePlay Maintenance in East Greenwich, Rhode Island. Connect with Art via email at aeddy@replaymaintenanceusa.com or phone (877) 641-1819.