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Timothy R. Derrick, Graham E. Caldwell and Joseph Hamill

A modified mass-spring-damper model was used to simulate the vertical ground reaction forces of a human runner as stride length was altered. Spring stiffness values were selected by an optimizing routine that altered model parameters to match the model ground reaction force curve to a runner’s actual ground reaction force curve. A mass in series with a spring was used to simulate the behavior of body structures that produce the active portion of the ground reaction force. A second mass in series with a spring-damper system was used to simulate the behavior of those components that cause the impact portion of the ground reaction force. The stiffness of the active spring showed a 51% decrease as subjects increased their stride length. The stiffness value of the impact spring showed a trend opposite that of the active spring, increasing by 20% as strides lengthened. It appears that the impact stiffness plays a role in preventing the support leg from collapsing in response to the increased contact velocities seen in the longer strides.

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Mohsen Shafizadeh, Nicola Theis and Keith Davids

running impact shock to their physical constraints in the same way as runners without disabilities attenuate impact shock during RaceRunning. Therefore, the purpose of the study was to determine the timing and frequency of impact shock and attenuation in people with motor disorders during 100-m