Absorption of energy during whole-body vibration exposure

Absorbed power, P-Abs, during exposure to vertical and horizontal whole-body vibration in sitting posture was measured using 15 male and 15 female subjects. Different experimental conditions were applied, such as vibration level (0.25-1.4 m/s(2)), frequency (1.13-80 Hz), body weight (54-93 kg), relaxed and erect upper body posture, Results show that P-Abs was strongly related to frequency of the vibration peaking, within the range of 4-6 Hz and below 2.5 Hz for vertical and horizontal directions respectively. P-Abs increased with acceleration level and body weight. If risk assessment is based on the assumption that the amount of P-Abs independence of the frequency of the vibration, indicates a hazard, then the frequency weighting procedure in ISO-standard 2631 can be questioned. The ISO weighting for horizontal vibration seems to underestimate the risk for frequencies within the range of about 1.5-3 Hz and overestimate them above about 5 Hz. For the vertical direction the frequency weighting overestimates the risk for frequencies above about 6 Hz. The results also indicate a need for differential guidelines for females and males. Many types of vehicle produce whole-body vibration with frequencies in the range where the highest P-Abs was observed. Although not yet thoroughly evaluated, P-Abs may be a better quantity for risk assessment than acceleration as specified in ISO 2631, since it also takes into account the dynamic force applied to the human body. (C) 1998 Academic Press.