The dynamic responses of the seated body exposed to vertical vibration are investigated at the two driving-points, formed by the upper body-backrest and buttock-pan interfaces in terms of force-motion relationships. The dynamic interactions of the seated body are characterized in the laboratory in terms of apparent masses at the two driving-points under white noise and track-measured random vertical vibration in the 0.5-40 Hz frequency range. The experiments were performed with 24 adult subjects seated on an idealized rigid seat, representing an automotive seat geometry. The vertical and fore-aft forces at the body-pan and body-backrest interfaces were measured to determine the apparent mass responses at the two driving-points. The results clearly revealed significant dynamic interactions of the upper body with the back support. The results also showed considerable influences of the vibration magnitude, body mass and the subjects’ hands position on the measured biodynamic responses.
