Biodynamic responses of lightweight, mediumweight and heavyweight subjects in seating posture exposed to single-axis vertical vibration

Lack of the biodynamic data of lightweight and heavyweight human bodies in seating posture becomes an impediment to developing dynamic dummies and relevant standards for improving vehicle ride comfort and reducing health risks caused by vibration. To acquire missing data and gain an understanding of relevant biodynamic responses, the vertical apparent masses of seated subjects in lightweight and heavyweight groups as well as the mediumweight group (targeted mass 55 kg, 98–115 kg, and 75 kg) were experimentally measured and studied under 9 vibration magnitudes (0.25, 0.315, 0.4, 0.5, 0.63, 0.8, 1.0, 1.25 and 1.6 ms⁻² r.m.s. with a common ratio of ca. 1.25) without and with the support of an upright backrest. Each group had twelve subjects. With an increase in the vibration magnitude from 0.25 to 1.6 ms⁻² r.m.s., the resonance frequency of the vertical apparent mass showed a decreasing trend. This was observed with all three bodyweight groups and two backrest conditions. Results of pairwise Wilcoxon signed-rank tests showed that, when the vibration magnitude increased by a factor of ca. 1.25, its effect on the resonance frequency was statistically insignificant in most cases. The results provided data on the vertical apparent mass for the heavyweight subjects that have not been reported and augmented the database of those for the lightweight subjects.