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Shock attenuation of the impact peak and overpronation are both considered important in running shoe design. A number of investigations indicate that both of these factors are related to various running injuries. These indications are mostly empirical or based on statistics and often show a lack of arguments to relate external measurements to internal loading of joints or muscles. The purpose of this paper is to present some relationships between impact peak, pronation, and forces at the subtalar joint and on muscles (which are in tension in pronation) during touchdown in rearfoot running. The calculations show that the material properties of the shoe sole (altered from Shore A20 to A50) largely influence the rearfoot movements during touchdown (increase in pronation velocity from 7 to 25 rad/s) and increase to some extent the muscle forces on the medial side (600 to 850 N) of the subtalar joint. In comparison, the impact peak (1550 to 1600 N) and the ankle joint forces (2500 to 2700 N) change very little. Hence, running shoe design should be focused more on the control of the rearfoot movement during touchdown and less on pure shock attenuation.
The authors are with the Biomechanics Laboratory of the Swiss Federal Institute of Technology (ETH), 8092 Zuerich, Switzerland.