GMAX Testing of Surface Hardness


Managing Surface Hardness


Managing surface hardness on synthetic turf athletic fields requires both routine GMAX testing and proper field maintenance. Approximately 15% of concussions in football and soccer result from the head impacting the playing surface. Head injury risk can be reduced by ensuring playing surfaces meet industry-established GMAX thresholds, contain proper infill amounts and receive routine maintenance.

Measuring Surface Hardness


Surface hardness is measured by determining the GMax of the playing surface. 

GMAX is a numerical value representing the hardness of the surface, with higher values indicating a harder surface.

The Clegg Impact Tester and the ASTM F355 device are tools commonly used to measure GMAX.

The NFL requires the Clegg Impact Tester be used to measure GMAX prior to every game. All areas within the field of play must be below 200 GMAX.