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INTRODUCTION: Injuries related to foot traction are ubiquitous ranging from insufficient traction (slip and fall) to excessive traction (failure to release causing fracture or soft tissue damage). The existing literature on computational modeling of the footwear/ground interaction is limited and focused primarily on musculoskeletal dynamics simulation (i.e., the load transfer through the body) rather than on transfer into the body (through the ground/foot interface). Hence, there is opportunity to develop and/or enhance techniques for modeling footwear traction to reduce injury.

RATIONALE: The most common NFL injury is to the foot and ankle region accounting for 26% of all reported injuries [1], of which a significant but unknown number are related to excessive traction. The goal of this research is to determine whether the discrete element method can simulate the interaction between turf and studded footwear. The long-term goal is to optimize the interface between footwear and artificial turf to provide the safest possible environment for athletic participation while balancing demand for dynamic traction against the risk of injury.

MATERIALS & METHODS: Three football studs were torqued to slip on artificial turf in a laboratory setting to provide validation data. The studded assembly was turned at 1 degree per second in artificial grass alone, rubber infill alone, and grass+infill artificial turf on a servo hydraulic load frame for 60 seconds. An increase of over 600% in both max and average torque was found when comparing grass+infill to just infill.

The bench results were used to calibrate a discrete element model of three studs. Subsequently, a series of simulations were run to determine the effects of stud geometry and pattern. The models applied 1 degree per second for 60 seconds or 2.58 meters per second for .4 seconds, as with published literature [2, 3]. Each model evaluated the torque/rotation load history and the force/translation history in two directions. The three load scenarios were repeated on four common stud shapes and three unique stud patterns. Filtered torque, force, and kinetic energy were evaluated as indicators of stud grip.

Results: Round, square and hex shape studs were compared in the rubber infill turf model. Peak torque increased 17% and 0.9% for the square and hex stud compared to the round studs. Mean torque over time increased 22% and 0.4%, respectively. Additional results comparing cleat patterns and turf condition will also be described.

DISCUSSION: Stud geometry appears to play a significant role in torque generation in artificial turf. Clinically, the results suggest that round studs may limit torque transfer and thus might reduce injury. However, the optimal balance between traction and release has not been established. Based on these preliminary results, the discrete element method appears to provide effective dynamic stud/turf interaction modeling and may be useful in a broader set of studies.

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