The aim of the present study was to define the multiple effect hand-arm vibration composed of four equally effective one-third octave band vibrations (63 Hz, 125 Hz, 250 Hz and 500 Hz) on the temporary threshold shift in vibratory sensation.
Seven healthy subjects were exposed to vibration by grasping a vibrated handle in a soundproof thermo-regulated room. The vibratory sensation threshold at 125 Hz was measured before and after vibration exposure at an exposed fingertip. At first we determined each acceleration of the component one-third octave band vibrations for each subject. These should induce the same magnitude of temporary threshold shift in vibratory sensation immediately after the vibration exposure (TTSv,0 as induced by the reference one-third octave band vibration (250 Hz, 4g). We measured TTSv,t for the exposures of the composed vibrations and the four component vibrations. TTSv,0 was determined for each exposure according to the exponential recovery model stated in the previous study.
The TTSv,0 induced by the composite vibration was not longer than that which might have been induced by each component vibration. This result confirms our previous speculation that the component of the vibration inducing the largest TTSv,0 determines TTSv,0 by broadband random vibration.