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FIELD SCIENCE r IT HAS BEEN SUGGESTED THAT A GMAX OF 150 TO 175 MAY BE MORE APPROPRIATE FOR F 1936-98 IF THE PLAYERS ARE HELMETLESS. ASTM standard tests the numerical data obtained by each tester cannot be compared.The ASTM has two standard test methods for measuring the shock- F 355 missile is said to simulate a head striking the playing surface absorbing ability of playing surfaces. The first is the primary method while the D 5874-02 missile has been described as an elbow striking itused on synthetic surfaces. This procedure is ASTM F 1936-98 the surface. Researchers at Penn State are trying to correlate the two 'Standard Specification for Shock-Absorbing Properties of North methods to one another. American Football Feld Playing Systems as Measured in the Field.' A very important difference between these two methods is that The second method is for use on natural turf and soil playing sur- ASTM uses the Gmax threshold of 200 for F 1936-98,but does not faces. It is ASTM F 1702-96, 'Standard Test Method for Measuring have a threshold for F 1702-96. It has been suggested that a Gmax Shock-Attenuation Characteristics of Natural Playing Surface Systems of 150 to 175 may be more appropriate for F 1936-98 if the players Using a Lightweight Portable Apparatus."The two methods have many are helmetless. A Clegg reading of about 125 may be a reasonable similarities. but the differences are important enough so that the upper limit for natural turf fields according to some university numerical results cannot be compared.or at least not at this time. researchers and values from 60 to 95 are regarded as acceptable. Both F 1936-98 and F 1702-96 use instruments called impact testers.These testers indirectly measure the hardness of the playing In the field surface by dropping a cylindrical weight, called a missile. down a ASTM 1936-98 covers testing for Gmax on synthetic North American guide tube onto the surface. Peak deceleration of the missile as it football fields.In this procedure six test locations are tested for hard- strikes the surface is measured. Figure 1 shows a typical impact ness with the F 355 impact tester.These test locations are based on tester used in each procedure. known field wear points. The test locations are: The impact tester used for synthetic turf has a 20-pound missile equipped with accelerometers.A computer captures the acceleration. Point 1-Goal Line, End A,Center Field. deceleration data for the entire impact.The 24-inch drop height came Point 2 - 10 Yard Line, End A, 1/4 the distance measured from from the automotive industry and the missile weight came from a sideline C to center field, Northwestern University study of helmeted middle linebackers during Point 3 - 25 Yard Line, End A, 1/2 the distance measured from actual play. With modification this test method can be used on sideline C to center field, wrestling mats, playgrounds. body padding, trampoline frame Point 4-50 Yard Line,Center Field, padding, goalposts, shoulder pads and gymnasium walls. Figure 2 Point 5 - 25 Yard Line, End B, 1/4 the distance measured from shows an impact curve for a 100%crumb rubber infill synthetic foot- sideline D to center field, ball field with no shock pad. Point 6- 12 Yard Line, End B,Center Field. The Clegg Impact Tester is an impact tester equipped with a mis- sile of approximately 5 pounds and a bottom face of approximately 3 Three missile drops are performed at each test location with each square inches. This missile is dropped from 18 inches. The Clegg drop being three minutes apart. Gmax data from the first drop, the ® Impact Tester results in lower Gmax values than the F 355 tester and 'conditioning drop', is disregarded but Gmax data from the second 14 May 2006 www.greenmediaonline.com