Vibration can enter the body of mobile equipment operators, the hands of workers using power-tools or the feet of workers standing on vibrating platforms (Eger et al, 2006). Epidemiologically, 4-7% of workers in Canada, the United States and the European Union are exposed to potentially harmful vibrations (Bovenzi, 1996). Mine workers drilling from stationary platforms are exposed to whole-body vibration above the eight hour health guidance caution zone set-out in ISO 2631-1 (Leduc et al, 2010). Literature suggests that the health effects typically observed in the hands have been reproduced in the feet when exposed to similar vibration frequencies and accelerations (Griffin, 2008). However, research associated with foot transmitted vibration (FTV) is limited despite evidence of negative health effects of vibration at the foot, either with direct segmental exposure (Thompson et al, 2010) or indirectly with hand-arm vibration exposure (Sakakibara and Yamada, 1995). Improved understanding of FTV is warranted, to deal with potentially harmful vibrations, which lead to injury, and to identify interventions capable of attenuating harmful vibrations at the foot.

The primary objective of study one (Chapter 2) was to determine the vibration transmissibility between the floor and the ankle when exposed to FTV. The transmissibility between the floor and ankle was compared between males and females and between different foot arch types to determine if there was a significant difference in floor-to-ankle vibration transmissibility. The second objective was to determine if there is correlation between floor-to-ankle transmissibility and participant reported discomfort scores. Sixteen university aged participants (eight males and eight females) participated in the study. The participants were exposed to two levels of vibration, while standing on a low frequency (3.15-lOHz) and a high frequency (40Hz) vibration platform. Vibration was recorded at the floor and the ankle with two tri-axial accelerometers in accordance with the ISO 2631-1 guidelines. Participants reported body discomfort on a 9-point discomfort scale following each vibration trial. Vibration recorded in the z-axis (vertical axis) entering the foot (Fawz) was compared to vibration recorded in the z-axis at the ankle (Aawz). The percentage difference between Aawz and Fawz was taken as a measure of vibration transmissibility from the floor through the foot to the ankle. There was a significant difference in floor-to-ankle vibration transmissibility (p= 0.001;​ F= 3.27) by vibration exposure frequency. The participants attenuated FTV when exposed to high frequency vibration;​ however, there was no significant attenuation of vibration during low frequency vibration exposure. There was no significant difference in the floor-to-ankle vibration transmissibility or discomfort by gender (p= 0.715), or foot arch type (p= 0.515).

Despite evidence to support their efficacy, many industries use mats and insoles believing they are capable of attenuating FTV (Leduc et al, 2011). Therefore, the primary objective of the second study (Chapter 3) was to determine the transmissibility of commercially available insoles and mining boots. Sixteen participants (eight males and eight females) experienced four insoles and two mining boot conditions at two vibration levels, while standing on a low frequency vibration platform (3.15-10Hz) and a high frequency vibration platform (40Hz). Vibration was recorded at the floor and above the insole/boot at the ankle with two tri-axial accelerometers in accordance with the ISO 2631-1 standard. The percentage difference between the vibration recorded at the ankle (Aa_wz) and the vibration recorded at the floor (Fa_wz) was used to determine vibration transmissibility of the insole/mining boot. A paired comparison of the insoles/mining boots was also done to identify the preferred insole/mining boot based on participant comfort reports (9-point scale) provided after each insole/mining boot condition. There was a significant difference in vibration transmitted from the floor through the insole (p= 0.00;​ F= 17.91) and boot (p= 0.014;​ F= 6.31) to the ankle by exposure frequency. All the insoles and mining boots attenuated vibration during high frequency vibration exposure;​ however, with the exception of mining boot 1 none of the insoles or mining boot 2 were effective in attenuating vibration during low frequency FTV. There was no significant difference in vibration transmissibility or reported discomfort between genders. The participants identified insole-3 and mining boot-2 as most comfortable when exposed to low frequency and high frequency FTV. Future studies should identify an effective bootinsole combination capable of attenuating vibration frequencies believed to contribute to potential health risks at the feet.