Assessing whole-body vibration transmissibility in children's bicycle trailers

Abstract

The overall objective of this thesis was to assess whole-body vibration (WBV) exposure in bicycle trailers to determine 1) vibration exposure characteristics associated with children riding in bicycle trailers, 2) the effectiveness of the bicycle trailer seat in reducing vibration transmitted to children riding in a bicycle trailer, and 3) to determine if gel seat cushions were effective in reducing vibration transmissibility through the seat/gel cushion to the buttock of a child in a bike trailer. These objectives were accomplished through a field study and a laboratory study. The first study, was conducted in the field with the primary objective to 1) to document vibration exposure characteristics measure on the bicycle trailer frame, at the interface between the seat and buttock of a seated child, and at the back of the child’s head, 2) to determine health risks based on an ISO 2631-1 health guidance caution zone (HCGZ) analysis, and 3) to determine if vibration exposure characteristics differed when riding on gravel compared to a paved terrain. The findings revealed an associated health risk, with levels of vibration measured at the buttock/seat interface consistently exceeded ISO 2631-1 health guidance caution zone guidelines. Moreover, vibration exposure magnitude, and associated health risk, was higher when the bicycle trailer was ridden on gravel terrain at higher speeds. When adjusted for a twohour exposure time, vibration experience by the children sitting in the bicycle trailer, for the majority of the trials, revealed a moderate health risk according to the ISO 2631-1 HGCZ. Additionally, all 12 trials had seat-to-head transmissibility levels above 1.00, indicating an amplification in vibration from the child’s seat to their head when riding in the bicycle trailer. The second study, was conducted under controlled laboratory settings with the aim to determine the impact of independent variables terrain type, trailer type, and cushion type, on dependent variable vibration magnitude measured at the interface between the trailer seat and simulated buttock of a child. Terrain type had the largest influence on vibration exposure levels (p<0.001), followed by trailer type (rigid-frame vs. suspension-frame) (p<0.001). Gel cushions did not significantly influence vibration measured at the seat/buttock interface but were found to reduce vibration measured at the rigid-frame trailer. Findings from this thesis suggest that if children were to spend greater than 2 hours a day in a bicycle trailer, they would exceed the ISO 2631-1 HCGZ, and ultimately be at an increased risk for a vibration-induced injury. Children were also exposed to higher levels of vibration when the bicycle and trailer travelled at a higher speed and travelled over rougher (gravel) terrain. Laboratory analysis found the gel seat pad was not effective at attenuating vibration at the seat. Additional research should be conducted with a larger sample of bicycle trailer types. Furthermore, this study highlighted the need for additional research to determine health risks associated with vibration exposure in young children as current international standards are designed to determine health risks of vibration exposure for health adults in an occupational context.