During its long-term usage, the human body is daily subjected to different set of loads; among them are the transient forces, which are characterized by large force transients over short periods. These forces, referred to in the literature as “Impact”, can cause short and long term damages. Impact on the human body was widely studied and its characterization is being continuously updated. In addition to the quantitative characterization of the ‘force wave’ attenuation along the body and its effects, there are continuous efforts to simulate the phenomena using dynamical models that provide a better insight and serve as a reliable research tool. Existing models of the human body for impact during vertical fall have been incomplete and have generally included “Lumped”, “Rigid-bodies”, and “Wobble-mass” models. 
The goal of this research was to set a mathematical model, which well reflects the impact stage, of a human drop. Since this model was defined up to a parametric level, a reliable parameter estimation procedure was also required. The model was based on both simulated and in-vivo experimental data.

Two 2D biomechanical models were examined: a 5-segment “rigid-body” model, and a comprehensive 8-segments “wobble-mass” model. The segments’ mass-inertia properties were evaluated using anthropometrics tables and analytical modeling methods.
The study included three “blocks”, corresponding to the different levels of the modeling stages: “Block-one”’ used a simulated (=”synthesized”) database to define and explore the basic analysis tools regarding parameter estimation and optimization procedure (e.g.: optimization algorithm, functional structure etc.). “Block-two” applied the general configuration of “block-one” to adjust the algorithm to the specific impact of the fall problem (e.g.: what model best represents the impact, etc.). ”Block-three” provided an explanation to some of “block-two” inaccuracies, and improved the algorithm to better perform. The final algorithm was tested on 27 files of six subjects’ experiments, indicating a consistent behavior, and was able to well replicate the three experimental measurements of the head acceleration, shank acceleration, and vertical ground reaction forces (VGRF).
The present model provides an established “wobble-mass” segmentation, and underlines the benefits to the impact phenomenon. The research also brings a reliable optimization algorithm to solve the unknown impedance parameters, backed by methodological examinations rather then previously used operational “finger rules”.
The research results can be implemented on impact studies, and its tools can be used in other fields of engineering.