Assessing the risk of vibration exposure during wheelchair propulsion

Although the exposure to whole-body vibrations (WBV) has been shown to be detrimental to seated humans, the vibration levels to which wheelchair (WC) users are exposed to in their communities have not been thoroughly examined. Furthermore, some evidence suggests that the cushions used in WCs, the first line of protection, may amplify WBV, although conclusive evidence has not been presented in the literature. The purpose of this work was twofold. First, to evaluate and compare the transmissibility of commercially WC cushions with two laboratory test methods: (1) direct measurement of transmissibility while human subjects propelled a WC over a road course with different cushions and (2) characterization of cushions with a material testing system (MTS) combined with mathematical models of the apparent mass of the human body. Second, to evaluate WBV exposure to WC users in their communities using ISO 2631-1 methods, and determine whether exposure levels are correlated with WC type and/or back pain, which is a physiological symptom of WBV exposures. Results showed that although dynamic characterization of WC cushions is possible with an MTS, the results did not correlate well with the transmissibility obtained in the WC road course. Significant differences were found for transmissibility among the cushions tested, with the air-based cushions having lower transmissibility than the foam- or gel-based cushions. All WC users who participated in this community-based trial were continuously exposed to WBV levels that were within and above the health caution zone specified by ISO 2631-1 during their day-to-day activities. Our evidence suggested that WCs with suspension did not significantly impact the WBV transmitted to WC users. Finally, we found that WC users are exposed to other risk factors to LBP such as prolonged sitting and transfers. WBV exposure to WC users may be an important contributor to LBP as it has been shown to exceed international standards. Suspension systems need to be improved to reduce vibrations transmitted to the users. More research is needed to understand the interplay between posture, WC configuration, and WBV