Transmission of vibration through the human body to the head

This thesis concerns the transmission of vibration through the human body and the effects of various sitting and standing postures on vibration at the head. Knowledge of the transmission of vertical vibration for seated subjects is well advanced, however, this is not the case for horizontal seat motion. Only a few previous studies have dealt with the transmission of translational (mainly vertical) vibration to the heads of standing subjects. Six axes of head motion have been measured for all experiments reported in this thesis.

Experiments conducted with seated subjects involved the investigation of intra-subject variability (repeatability) and inter-subject variability in the transmission of vibration from seat to head. The effect of contact between the subject's back and seat backrest on transmissibility has also been determined. Inter-subject variability was much larger than intra-subject variability and, in some cases, transmissibility between subjects varied by as much as 20:1.

Laboratory experiments conducted with standing subjects determined intra-subject variability and inter-subject variability in floor-to-head transmissibility and the effect of different body postures on head motion. Head motion occurred mainly in the mid-sagittal plane during exposure to both x- and z-axis floor vibration; lateral floor vibration resulted in mainly lateral head motion. Holding a handrail or standing with legs locked at the knees generally resulted in more head motion than with no hand grips and legs bent postures.

Measurements of head motion of a subject seated in an off-road vehicle traversing rough terrain showed that vibration in both x- and z-axes mostly caused head motion in the x-, z- and pitch axes. Lateral seat vibration mainly affected lateral axis head motion. Roll and pitch motion at the seat had only a small effect on head motion. (Abstract shortened by UMI.)