When a player falls, the impact is absorbed either by the playing surface or the player’s body. The “harder” the surface, the greater the amount of the impact absorbed by the player’s body; and, not surprisingly, the greater Concussions are a common injury the likelihood the fall will result in injury. This is especially true with respect to concussions – traumatic injuries to the brain – which can occur when the player’s head hits the playing surface. Concussions are an insidious form of injury. The effects of individual concussions are most often fairly mild. In the case of multiple concussions, however, the effects can be cumulative and the consequences can be long lasting – even permanent. Additionally, if a player has already experienced one concussion, they are more likely to experience another; and subsequent concussions carry a much higher risk of serious injury – up to, and including, death. If for no other reason than to lessen players’ exposure to this type of injury, it is important to monitor the impact-related characteristics of sports surfaces.
Impact testing (commonly referred to as Gmax testing) is used to measure the shock-absorbing properties of sports surfaces – including synthetic (artificial) turf and natural turf athletic fields. Gmax values express a ratio: the ratio of the maximum acceleration (deceleration) experienced during an impact, to the normal rate of acceleration due to gravity. The higher the Gmax value, the lower the shock-absorbing properties of the surface. Gmax measurements are a fundamental tool of athletic field safety testing. They are also useful in assessing the playability of a field.
Gmax testing involves measuring the shock absorbing properties of a playing surface in situ, and comparing the results against a standard. The most commonly used standard is the one established by ASTM
International (ASTM). For synthetic surfaces, ASTM specifies that the reported Gmax value for all test points on a field should be less than 200 Gmax (as measured in accordance with ASTM procedures F355-A and F1936). If the standard isn’t met, the field is considered unsafe and remediation is required.
While the maximum threshold value of 200 Gmax is the de facto standard for evaluating the safety of an artificial field, many architects set different standards for the fields they design. These alternate standards typically involve a range of acceptable Gmax values. The range sets an upper limit that addresses safety, and a lower limit that focuses on playability. The operative assumption is that fields that are too “hard” are dangerous, while fields that are too “soft” contribute to excessive fatigue and poor player performance. The range of acceptable values will vary in accordance with the materials and methods used to build a field, and also as a matter of the architect’s personal preferences.
