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This report summarizes a series of studies which address the compromise between high translational and low rotational traction in the development of cleated shoe outsoles. In translation, a soccer shoe outsole must possess a coefficient of friction greater than 0.8 when forces are exerted in an anterior direction in order for the frictional forces to counter the high shear forces developed by a rapidly stopping foot. This can be achieved by molding outsoles from compounds such as styrene-butadiene rubber or by adding cleats as short as 2.6 mm to the outsole. If peak moments resisting rotation of a soccer shoe outsole could be reduced to values less than 30 N.m, the incidences of skeletal injuries may be reduced. It was also found that the classical laws of Coulomb friction do not apply to conventional soccer shoe outsoles. Coefficients of friction decrease with increases in normal pressure. This relation can possibly be exploited in future designs to reduce the compromise between translational and rotational traction.
playing fields, translational traction, rotational traction, artificial turf, ground reaction forces, coefficient of friction, cleat length
Biomechanics researcher, NIKE Sport Research Laboratory, Beaverton, OR