A study of the mechanical impedance of the human body at low frequency by continuous monitoring techniques

The mechanical acceleration-based impedance was measured primarily in the seated posture using a sweep of the sinusoidal input motion from 3 to 30 Hz, the subject's legs being supported. This posture was adopted as it was thought that it best simulated the seated passenger in a vehicle. The input force being in the direction of the longitudinal axis of the body, i.e. the measured force and acceleration being in the direction as specified in the ISO Recommendations (1969). To complete the study measurements were made on a small number of subjects in: (a) performing a tracking task in the seated posture while being vibrated; (b) three different standing postures, to try to assess the vibration-isolation qualities of the legs. Previous researchers have in their determination of whole-body mechanical impedance, used a steady frequency and have plotted the force and velocity input to the body, digitised these plots, and computed the impedance modulus and phase angle with a digital computer, this procedure being repeated at different frequencies in steps of ¼ or ½ Hz. The object of this research programme was to obtain a continuous plot of the impedance modulus against the input frequency of the applied vibration during the experiment.