Effect of the shoe sole on the vibration transmitted from the supporting surface to the feet
Vibration transmitted through the foot can lead to vibration white feet resulting in blanching of the toes and disruption of blood circulation. Controlled studies identifying industrial boot character-istics effective at attenuating the vibration exposures are lacking. Twenty-one participants ran-domly stood on the different materials secured to a vibrating surface. Transmissibility through the materials to 10 locations on the foot was measured across the frequency range 10-200 Hz. Ques-tionnaires were used to evaluate the comfort of each material. The materials were less effective at attenuating vibration transmitted to the toe region of the foot then the heel. The transmissibility to the heel reached a high of 1 between 10-20 Hz and a low of 0.3 between 150-200 Hz. Between 10-20 Hz all outsoles resulted in an average transmissibility of 0.9 and all insoles 0.8 with the greatest transmissibility reduction occurring between 20-50 Hz when standing on an air insole. The average transmissibility for the first toe was 1 between 10-50 Hz and increased to 1.4 between 100-150 Hz. At the first toe, none of the PPE reduced transmissibility between 100-150 Hz. There was a poor correlation between the vibration transmissibility and the subjective evaluation of comfort. Future research are needed to identify materials effective for protecting both the toe and the heel regions of the foot. Specific standards for shoes testing are required as well.