Analysis of whole-body vibration during manual wheelchair propulsion: A comparison of seat cushions and back supports

The transmission of vibration to an individual during manual wheelchair propulsion can lead to injuries such as decubitus ulcers and low-back injuries. Based on the accelerations measured at the wheelchair/seat cushion interface and a bite-bar held by the individual, the transmissibility was calculated both in the time domain and in the frequency domain. The transmissibility was measured for both individuals without a disability, and for individuals with a disability who use a wheelchair as their primary mode of mobility. The parameters which proved most useful in detecting differences among the seat cushions and back supports were the vibrational-dose-value transmissibility (T), the frequency corresponding to the maximum magnitude of the transmissibility in the frequency domain (F_max), and the frequency-domain transmissibility in the frequency domain (H_oct). In general it appears that the best (worst) seat cushion and back support are dependent on the individuals who are propelling the wheelchair (i.e. individuals with a disability versus individuals without a disability) and the type of analysis (i.e. time domain versus the frequency domain). Overall, the time domain transmissibility for the individuals without a disability was used to determine the best and worst seat cushion and back support. This was due to the fact that the results were consistent, the statistical model adequately accounted for the wheelchairs, and the individuals did not have a preconceived bias. The best seat cushions are the Varilite Solo followed by the Jay Active while the worst seat cushions are the Pin-Dot Comfort Mate and Roho Low Profile. The best back support was the Varilite Fast Back while the worst back supports are the Sling Back and Jay Active Back. For individuals with a disability, the best seating system (lowest time-domain transmissibility) performed better than the individual's own seating system for each individual obstacle and all of the obstacles combined. Differences among the seat cushions and back supports seem to be due to the material properties as well as stability provided by the seat cushion. Future analyses should concentrate on the wheelchairs themselves, as well as the components that make up the wheelchair assembly (i.e. frame type, casters, tires, etc.).