Effect of non-neutral seated postures on whole-body vibration measurements

ISO 2631-1 generally treats frequency-weighted acceleration measured at the seat-occupant interface as independent of operator posture, yet this assumption has rarely been examined explicitly. This study evaluates that assumption. Twenty-four participants were exposed to three-dimensional whole-body vibration on a machine operator seat while maintaining forward lean, reclined, and twisted postures. Despite constant base excitation vibrations, the seat-interface frequency-weighted RMS acceleration (FWRMS) differed significantly across postures (F = 0.871, R = 0.765, T = 0.845 m/s²; p < 0.001), with posture explaining 78% of variance. A sandbag surrogate experiment confirmed that body-weight redistribution alone, without neuromuscular involvement, produced an approximately 13% variation in FWRMS, linking postural load shift to altered seat suspension dynamics. When propagated through ISO 2631-1 exposure equations, this corresponds to an approximately 27% difference in allowable daily exposure duration. These findings highlight the need to incorporate posture into whole-body vibration standard 2631-1 and occupational vibration risk assessment.