The aim of this dissertation was to develop a multibody computer model that simulates the dynamic response of a human lower limb when subjected to plantar impact and predicts hard and soft tissue injury. Existing constitutive data were used when available, but most of the model parameters were experimentally determined as part of this study.

Experimental efforts focused on the role of the Achilles tendon during plantar impact, the mechanical structural properties of the ankle ligaments, and the role of the fibula during dynamic and quasistatic loading. A new method for in-situ measurement of Achilles tendon tension was developed and validated. The passive involvement o f the posterior leg muscles was characterized for quasistatic and dynamic conditions. Nonlinear viscoelastic properties of eight of the hindfoot ligaments were characterized using a force relaxation test for the unpreconditioned and preconditioned states. The fibula was found to be loaded primarily in bending, contrary to current conceptions in the literature.

The lower extremity multibody model was created in MADYMO. Anthropometric and inertial properties were obtained from published military and civilian research as well as from cadaver studies conducted as part of this research. Nonlinear viscoelastic elements were incorporated in the multibody model to simulate the force relaxation characteristics of viscoelastic structures. The model was validated with two plantar impact scenarios representing different ankle orientations, peak forces, and force onset rates. The results of this research provide new tools for experimental testing of cadaveric specimens, a new paradigm on the role and extent of fibula loading, viscoelastic characterization of eight hindfoot ligaments, and a multibody model for investigating plantar impact injuries to the human lower extremity.