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GMAX Testing


GMAX testing is a test fundamentally designed to ensure that a synthetic-turf field is performing the way it should with respect to impact attenuation or shock absorption.

  • It measures how many G’s of force a field can absorb upon impact, and how many are returned to the athlete.

  • A high GMAX test value means the field is absorbing less impact, and returning more force to the player (resulting in a potentially dangerous situation), than a low GMAX test value.

  • The American Society for Testing and Materials standard test consists of a guide tube that’s about 2.5 feet tall and a 20-pound, cylindrical weight that falls through the tube. An accelerometer mounted on the weight measures how rapidly the missile decelerates or stops.

  • That flat-faced “missile” is connected to a small device that records the velocity as the missile hits the surface, the G-forces that are experienced during decelerations, and more.

  • GMAX performance on a synthetic field can vary based on the amount and composition of infill material, how much the carpet has worn over time and whether the infill material has become contaminated.

  • Concussion safety is one reason for GMAX testing. But it’s more focused on determining the risk of skull fractures and broken bones.

How often should you test? 


It is important to note that g-max measurements are not static. On synthetic turf surfaces, g-max values will generally increase as the field ages. The amount of the increase, and the rate at which it occurs, are tied to construction methods, materials used, levels of play, environmental conditions, and the frequency and types of maintenance. This suggests that regular g-max testing is important - but how often is often enough? Everyone agrees that new synthetic fields should be tested before they are accepted from the builder. Beyond that, opinions differ: some advocate testing at least twice a year; some suggest an annual test; others say that testing can be less frequent. Among researchers and other industry experts, there is a general consensus that an annual test is most desirable:

  • Annual testing demonstrates a serious and proactive commitment to safety

  • Fields rarely become unsafe overnight, so testing once a year should provide adequate warning of emerging safety issues

  • Significant changes in g-max readings can be an early sign that problems are developing within the turf system - an annual test can alert you to these problems before they become critical

  • Annual testing generates a meaningful historical record - a record that can be important if warranty or liability issues arise

  • Testing more than once a year isn't a "budget buster"

Click images for details

Department of General Services:

  • Provide testing at selected DCPS/DPR athletic fields; provide GMAX turf Assessments and Evaluations.

Wilson Senior High School

Portfolio: GMAX Testing
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