Despite much research into human response to whole-body vibration, there exists only a limited basic understanding - insufficient for any reliable prediction of response to a particular vibrational environment. It 1S argued that a viable explanation of human response to vibration is depende-nt on an adequate understanding of the complex biomechanica1 behaviour of the body. Further, knowledge of the degree of linearity of biomechanica1 frequency response is important if behaviour is to be under- stood and capable of prediction or application to system design. The aim of the research was to investigate the linearity of response and develop a reliable technique for the investigation of biomechanica1 response to vibration, the technique being simple and safe to apply to individuals in a variety of postures and eliciting results relevant to practical situations. A further aim was to investigate -how far posture might modify the bio- mechanical behaviour.

A variety of stimuli, response functions and analysis techniques were investigated, and a pilot study used to test their relative values. The method which was developed made use of a random vibration stimulus and linear transfer-function analysis applicable to stochastic signals. The method proved to be very suitable for practical application - a 51 sec. exposure giving reliable results. Data analysis took into account ·the frequency dependent characteristics of the measurement-chain, from transducer to computer.

It was found that the 'apparent mass' frequency response function gave reliable results, so that for short periods of exposure the human system could be considered linear and time invariant with observed coherehce function values in most cases greater that 0.95 between 0.4 Hz and 25 Hz, and 99% confidence limits for response magnitudes of the order of 0.2 dB. Transmission of vibration to the head was also investigated. This was found to be less reliable due to the nodding motion of the head, however, this could be improved by judicious transducer placement on each individual.

Although the response of an individual in a particular situation changed little, changes with posture were observed. Inter-subject variability was high and no general pattern of response allied to posture could be detected. tt was considered that an important parameter was the detailed configuration of the lumbar spine, this being very difficult to measure or control.

The simplicity of the technique, the relevance of the apparent mass function to the lumbar spine and the linearity of response at normal vibration levels have important implications. Changes in spinal loading during long periods of exposure can be examined;​ linear predictions of severity and simple weighting methods are vindicated;​ tissue characteristics are normally linear and non-linearity can be used as an indicator of damage risk.