Experimental response of the human body to a known periodic force as a measure of ballistocardiographic fidelity.

a very stiff and a very weak, light support were used. Close correlation was obtained between body displacement and light support displacement; body motion greatly exceeded that of the stiff support. Single mass resonant frequency was set by the dorsal skin stiffness when the support was very stiff and by the support stiffness when the light support was used. With both supports the body exhibited multi-mass motion in the frequency range above 6 c.p.s.