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Timely cardiopulmonary resuscitation (CPR) is often unsuccessful. The outcome can be improved by a better understanding of the relationship between the force applied to the sternum and the resulting hemodynamic effects. The first step in this complex chain of interactions is the mechanical response of the chest wall to cyclical compressions. A dynamic mechanical model of the chest response was formulated, and a method of identification of the model parameters based on force, displacement, and acceleration data acquired during cyclical compressions was developed. The elasticity, damping, and equivalent mass of the human chest were estimated with a constrained nonlinear least-mean-square identification technique. The method was validated on data acquired from a test apparatus built for this purpose. The model fit was measured with the normalized chi-square statistic on residuals obtained between recorded force and force predicted by the model. In the analysis of one human chest, the elasticity was found to be nonlinear and statistically different during compression and release.