Pergamon Press, now Elsevier
Journal of Biomechanics
A lumped-parameter model of the human body in the sitting position is formulated which includes the head, vertebral column, upper torso, abdomen--thorax viscera, pelvis, and legs. The differential equations of motion for the rigid-body representation of the isolated masses were written for nonlinear springs and dashpots which represented the elasticity and dampening, respectively, of the physical system. Also included in the equations of motion were coulomb friction forces for modeling sliding surfaces and related muscle contractions in the body, and the ballistocardiographic and diaphragm muscle forces. With all motions restricted to the vertical directions and sinusoidal displacements of the seat as the inputs, excellent agreement with mechanical and subjective experimental responses was achieved. Additionally, in agreement with the frequency dependency of muscle forces, the possibility of frequency dependent dampening coefficients was implied.