Vertical Deformation Testing For Foot Impacts
When athletes’ cleats dig into artificial turf fields thee stability under foot is key. You want a firm, supportive surface that is fast and fun the play on. Vertical deformation is how much the field is deformed when run upon, and is generally the “softness under foot” test. These measurements are important because if a surface is too soft an athlete risks ankle, knee, and other joint and soft-tissue injuries. If the surface is too hard we run into the issues like concussions or impact injuries that we tested the field for with the Gmax and HIC tests. Brock systems are stiff panels, shown by their ability to spread the running load out over a much greater area, so they provide a firm platform for the field. But the top surface “pistons” are engineered to allow for the right amount of deformation during running.
Brock uses a Deltec Field Tester (the offspring of the Artificial Athlete) to determine the deformation that occurs on a field. This test helps us determine the “Sweet Spot” for a fields firmness and impact absorption. The test measures the compression of a field in millimeters as it drops a spring loaded flat impacter 3 times in the same location. Natural grass fields see a result of 6-11 mm. Artificial turf fields over stone see less vertical deformation than natural grass fields, which makes them firmer to run upon, but can cause unacceptable injury rates for concussions and other body impacts. Turf over brock ranges between 7-11 mm, depending on the type and amount of infill in the turf, making it mimic the feel of pristine natural grass.
Deltec Field Tester
This test simulates the heel strike of an adult running athlete in stride.
Designing Artificial Turf Fields to Meet Deformation Standards
Although concussions have dominated the news when it comes to field sports, ankle and knee injuries are often the most common injuries among all athletes, according to stopsportsinjuries.org. These include sprains, strains, ligament tears, and a number of other joint and muscle injuries. In order to prevent these types of injuries it’s important to start from the ground up.
THE RIGHT BALANCE OF FIRMNESS AND SAFETY
Artificial turf fields offer a number of advantages to natural grass when it comes to playing surface injuries. You are able to control the feel underfoot for the entire field and are not combatting naturally occurring sinkholes, divots, or even rodent holes which can cause severe injuries. Installing a Brock shock pad system under your turf allows the fast, firm feel of running on a hard surface, but lessens the risk of injury when players fall down. The Brock panels were engineered with shock absorbing pistons that compress and recover. This helps the athletes gain traction, but also prevents the pad from compressing further than necessary. The delayed return doesn’t “spring” the energy back to the player, which can create a “bouncy” surface during running.
Beyond Deformation Testing: Testing for Head Injury Criterion & G-Max
There are three measurements used to characterize safety and performance of a surface
HIC is the internationally recognized test standard for head injuries. It drops a 10 lb hemispherical impactor from increasing heights to determine Critical Fall Height. It’s the same test used in playgrounds, automotive crashes, wall padding, pole vault, and the WR Reg22 standard for artificial turf. The higher the Critical Fall Height, the more protective the surface is for head injuries.
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This test method covers the measurement of certain shock-absorbing characteristics, like during body impacts. It’s applicable to natural and artificial playing surface systems. It does not correlate to head injury. It drops a 20 lb flat missile from 24”. GMax is a good measurement when used in conjunction with HIC above, but as a stand alone test is not a total measure of field safety.
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