Journal of the Society of Biomechanisms

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Leg stiffness, corresponds to the spring constant in the spring-mass model of running behavior, suggesting that increasing leg stiffness is an effective training strategy. Although running with forefoot strike pattern is associated with greater leg stiffness when measured without considering the translating of the center of foot pressure (CoP) during the stance phase, more rigorous measurement methods are needed to validate the results. In this study, leg stiffness was measured in 8 forefoot and 9 rearfoot strike well-trained runners based on two different methods: one based on actual center of mass (CoM) position and CoP position during running, and the other without incorporating CoP translating. The difference in leg stiffness between two method (Δleg stiffness) was calculated and Δleg stiffness between groups was examined using t-test. The results showed that Δleg stiffness was significantly greater (p < 0.05) in rearfoot strike runners. These results indicate that leg stiffness without incorporating CoP translating during running is underestimated, especially in runners with rearfoot strike patterns. In addition, a comparison of 17 well-trained runners and 14 untrained runners showed that leg stiffness based on actual CoM and CoP position was significantly greater (p < 0.05) in the group of well-trained runners, confirming that leg stiffness is still a running performance factor, even when the influence of foot strike patterns is excluded.

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