Seat & footrest vibrations in manual wheelchairs

Newer manual wheelchairs have incorporated suspension systems in the hopes of decreasing harmful shock and vibration transmission. This study examined differences in the shock and vibration transmitted to a manual wheelchair occupant with and without suspension caster forks and with and without rear suspension systems. Significant differences were found in the peak accelerations at the seat (p = 0.0004) and footrest (p = 0.0007) between the wheelchairs when using the OEM caster forks versus the suspension casters. The wheelchairs with suspension had significantly different frequencies at which the peak accelerations occurred for both the seat (p = 0.01) and footrest (p = 0.0001). The wheelchairs that had the suspension caster forks had lower total power per octave than the wheelchairs with the OEM caster forks. For the footrest vibrations, significant differences were found between the types of caster forks for all octaves except those associated with frequencies above 78.75 Hz. There were significant differences for wheelchairs with and without rear suspension for total power per octave of seat vibrations in the octaves between 7.81 Hz and 9.84 Hz (p = 0.01), and 12.40 Hz. and 15.63 Hz (p = 0.008). Suspension caster forks reduce the shock and vibration exposure to the user of a manual wheelchair. Rear suspension systems reduce some of the factors related to shock and vibration exposure, but they are not clearly superior to traditional designs.