Absorption of energy during vertical whole-body vibration exposure

Absorbed power ( P Abs) during exposure to vertical whole-body vibration in a sitting posture was measured on 15 male and 15 female subjects. Different experimental conditions were applied, such as vibration level (0.5–1.4 m s -2) and frequency (2–100 Hz), body weight (54–93 kg) and, relaxed and erected upper body positions. Results show that P Abs was strongly related to the frequency of the vibration, peaking within the range of 4–6 Hz. The peak was predominantly located in the lower end of this range for females and for the relaxed sitting position. P Abs increased with acceleration level and body weight. Almost a ten-fold increase in P Abs was observed at the critical frequency when the vibration exposure was raised from 0.5 to 1.4 m s -2. If risk assessment is based on the assumption that the amount of P Abs, independent of the frequency of the vibration, indicates a hazard, then the ISO-standard 2631 under- and overestimates the risk at frequencies below and above about 6 Hz, respectively. The results also indicate a need for differentiated guidelines for females and males. Many types of vehicles produce whole-body vibration with frequencies which coincide with the range where the highest P Abs was observed. P Abs is a ‘new’ concept for measurement of whole-body vibration exposure. Although not yet thoughly evaluated, this measure may be a better quantity for risk assessment than those specified in ISO 2631 since it also takes the dynamic force applied to the human body into account.