Comparison of the apparent mass of the seated human measured using random and sinusoidal vibration

Exposure to whole-body vibration is generally accepted as being a risk factor for low back pain and therefore exposure to vibration should be minimised. The results of previous laboratory based research investigating the biomechanical response of the seated human to vibration has been used to develop models that can be used within tools that are capable of predicting the response of seats. Several studies in the literature have reported apparent masses of seated human subjects whilst exposed to either random or sinusoidal vibration. Although these studies have shown similar trends, there have been no systematic comparisons of apparent mass for the same subjects exposed to random and sinusoidal vibration. This paper reports a study where twelve male subjects were exposed to random whole-body vibration at 1.0 m/s2 r.m.s. and to sinusoidal vibration at 1, 2, 4, 8, 16 and 32 Hz. The modulus of the apparent masses were nominally identical when measured using random or sinusoidal vibration. The phase of the apparent masses were similar at 1, 2 and 4 Hz, when measured using random or sinusoidal vibration, but showed consistent differences at 8, 16 and 32 Hz. As the results between experiments using different waveforms are similar, models derived from experimental work based on one type of stimulus could be applied in scenarios involving the other type of stimulus.