Temporary threshold shifts in fingertip vibratory sensation from hand-transmitted vibration and repetitive shock.
Level 2 - randomized trial
Randomized controlled laboratory trial in humans
PubMed 8494776 · doi:10.1136/oem.50.4.360
What was done
Human subjects held a handle at 10% maximum voluntary grip force and were exposed for 5 minutes to vertical 100 Hz continuous vibration or repetitive shocks of equal energy content (formed from single cycles of a 100 Hz sine wave). Exposures tested repetition rates of 5, 25, 50, or 100 shocks/s across three frequency-weighted root-mean-square acceleration levels (2.5, 5, or 10 m/s² rms according to BS 6842 and ISO 5349), compared with a no-vibration control. Temporary threshold shifts (TTSs) in fingertip vibrotactile perception were assessed.
What was found
Five shocks per second at all three frequency-weighted acceleration magnitudes produced small temporary threshold shifts, whereas 100 shocks per second (continuous vibration) produced large temporary threshold shifts despite identical frequency-weighted total energy. The relationship was quantified by the regression equation: TTS = -16.256 + 11.812 log10(R) + 15.179 log10(ahw), where R is shock repetition rate and ahw is frequency-weighted rms acceleration.
Why it matters
The findings demonstrate that the equal energy hypothesis used in ISO 5349 and BS 6842 is inadequate for predicting temporary vibrotactile sensory impairment from repetitive shock.
Limits
The abstract omits sample size, participant demographics, exact pre- and post-exposure threshold values, and standard errors. The experiment evaluated only brief (5-minute) acute exposures at a single frequency (100 Hz), so results cannot be directly extrapolated to chronic vascular or neurological damage from long-term occupational exposure.
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