Biomechanics of Seating: Body Posture, Loading and Friction in Office and Wheelchair Settings
Abstract (summary)
Sitting for long periods of time has health implications; two populations affected by long durations of the seated position include office workers and wheelchair users. In office workers, poor posture combined with long hours of sedentary periods can lead to cardio-vascular diseases, musculoskeletal disorders, and other health issues. The use of a standing desk is an alternative that can break up those sedentary periods. But workers find it difficult to use standing desks regularly, one of the reasons being pain associated with standing. Thus, there is a need for developing an alternative working position which provides an opportunity for postural change. Similar to office workers, wheelchair users are also prone to various health issues including pressure injuries (PIs), which put considerable financial and physical burdens on the user. One of the factors that increases the risk of PI formation is shear loading and associated frictional forces. Thus, there is a need to study how the choice of fabrics used for the seat pan cover and pants worn by wheelchair users affect the frictional properties and shear forces at the seat interface.
The objectives of this works were: 1) to evaluate changes in body position, body loading, and blood perfusion while in a seated, standing, and new office seating position, termed the in-between position. 2) determine the coefficients of friction of seven commonly worn pant fabrics and two seat cover fabrics using a mechanical device and a tilting seat pan 3) to determine the shear force and coefficients of friction between five commonly worn pant fabrics and two seat cover fabrics through the development and utilization of a novel in-vivo experimental set up that permitted sliding of the human buttocks on the seat pan.
To achieve the first objective, positions of anatomical landmarks, ground reaction forces, and blood perfusion data were obtained and analyzed during three different working positions: seated in a chair, standing, and a new ‘in-between’ position. Data showed that the in-between position provided a hip and lumbar position closer to standing than the seated position. Additionally, it provided less loading on the legs in comparison to standing. There were no significant differences in anterior/posterior ground reaction forces between seated and the in-between positions. Additionally, blood perfusion increased during dynamic transitions between positions indicating changes in blood flow.
To achieve the second objective, a mechanical device with the pant fabrics attached was placed on top of a seat pan. The system was tilted until the device started sliding on the seat pan. Positional data during the sliding was captured using the motion capture system and was used to calculate the coefficient of friction. The office fabric seat cover produced smaller coefficients of friction than the vinyl seat cover for all the pant fabrics. Women’s khakis demonstrated one of the smallest coefficients of friction, and denim demonstrated one of the largest coefficients of friction with both seats covers.
To achieve the third objective, individuals were asked to sit on a wheelchair-like seat while wearing the pant fabric to be tested. A linear actuator pulled them towards the front of the seat pan, so they were sliding across it, while the forces on the seat pan and the actuator were recorded by load cells. The ratio of these forces was used to calculate the coefficient of friction. The vinyl cover exhibited higher coefficients of static friction in this study as it did with the mechanical system.
Overall, this body of work provide a knowledge basis that will be useful in design of better office workspace and develop strategies that can reduce the risk of PI formation in wheelchair users.
Indexing (details)
Public health;
Occupational safety
0354: Occupational safety
0573: Public health
