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Abstract-The objective of this study was to describe the in-seat movement and weight-shifting behavior of full-time wheelchair users. We measured everyday sitting behavior for 192 d across 28 individuals who used manual wheelchairs as their primary mobility device. To obtain the measurements, we used eight thin force sensors placed under participants' wheelchair cushions. On a typical day, participants spent an average of 10.6 +/- 3.0 h in their wheelchair and transferred out of the wheelchair 8.4 +/- 4.3 times. Participants only performed pressure reliefs (90% off-loading of the entire buttocks for at least 15 s) 0.4 +/- 0.5 times per hour they were seated in the chair, but they performed weight shifts (WSs) (30%-90% off-loading of at least one side of the buttocks for 15 s) with a frequency of 2.4 +/- 2.2 times per hour. Despite the higher frequency of WSs, they were not performed in a routine manner. Half of the days studied included one segment of upright sitting lasting at least 2 h without a WS. Given these observations, we conclude that seating evaluations should emphasize positioning individuals in a way that facilitates reaching, leaning, and transferring in a safe manner, not only to improve function but also to affect buttocks loading.
Key words: activity, behavior, buttocks, interface pressure, monitoring, pressure relief, pressure ulcer, sitting, spinal cord injury, weight shift, wheelchair.
Abbreviations: COP = center of pressure, PPI = peak pressure index, PR = pressure relief, PRM = pressure relief monitoring, SCI = spinal cord injury, WS = weight shift.
INTRODUCTION
For many wheelchair users, the combination of reduced mobility and impaired sensation results in a life-time risk of developing pressure ulcers. In addition to the medical costs, the development of a pressure ulcer adversely affects activities of daily living, employment, and overall quality of life.
The formation and underlying causes of pressure ulcers are quite complex, with multiple influencing factors. However, tissue loading is the defining cause of pressure ulcers and distinguishes them from other insults such as vascular and ischemic ulcers [1-2]. The mechanisms by which tissue loading leads to tissue breakdown have not been established [3], but current theories suggest that a combination of cell damage from prolonged deformation, ischemia of soft tissues, and a disruption in the...