Goal of the Study?
In this case-control pre-publication study from the Ergonomics Journal1 the authors’ goal was to determine whether the chest support and armrests of a prototype chair mitigate the loss of seated height commonly seen during prolonged sitting compared to a traditional configuration of the same chair. Secondary outcomes explored differences in perceived pain, spine posture, seat pressure variables and various qualitative perceptions of support, comfort, stiffness of the offloading prototype chair compared to the control chair.
Why are they doing this study?
Sitting for prolonged periods of time causes sustained compressive loading of the Intervertebral Disc (IVD). This can result in cellular degradation, altered facet mechanics and pain. In addition, the static nature of sitting can impair the nutrient supply since IVD’s rely on changes in the hydrostatic pressures to bring nutrients and remove waste products. These degradations are amplified if the occupation or task at hand requires a more forward-leaning posture and discourages frequent breaks from the seated position.
A limited number of prototype chairs have been designed to address the challenges of offloading the spine compression during prolonged sitting, but this is the first quantitative and qualitative study to assess the effectiveness in reducing seat height compression and perceived comfort from prolonged sitting.
What was done?
Stadiometry is a measure of a person’s vertical height. Using this tool has revealed reductions in vertical height with as little as five minutes of sitting. This study recruited 20 male participants and exposed them to two chair configurations in a random order to either a saddle seat orientation (control) or the spine offloading prototype chair configuration. To control for other variables, the participants’ two trials were scheduled for as soon as they woke up and at the same time of the day and at least 24 hours apart. A series of accelerometer measurements of spine angles and a series of seat pressures were taken in 15-minute intervals for a period of 1 hour while playing a video game, Fortnite. Their sitting vertical height was measured using a stadiometer before and after. At the end of the hour, a series of qualitative surveys were used to evaluate their sitting experience.
What did they find?
The most significant finding was the reduction in seated spine height with the prototype chair (US Patent US:16453845) compared to the control saddle seat. Spine height loss over one hour of sitting in the offloading chair was 0.75 mm while the saddle seat height loss was 6.16 mm. There were no differences in spine angles or perceived back and gluteal pain between configurations. Seat pressure contact area and average pressure were found to change significantly over time in both chair configurations. Although peak seat pressure was not significantly different between the two configurations, the seat pressure contact area decreased over time with the offloading chair configuration and increased over time with the control configuration. Average lumbar and pelvic angle and pain ratings were found not to be significantly different between the two chairs.
Why do these findings matter?
Sitting for long periods of time is associated with an elevated risk of physiological disorders such as obesity, high blood pressure and potential declines in physical function and overall well-being. Previous studies have attempted to find effective means of recovering spine height loss after prolonged sitting. This study was designed to measure the preventative effects that an offloading chair can have in reducing spine height when compared to a saddle seat. A comparison to a traditional chair would likely see an even greater difference in seated height and posture.
Jerome Fryer DC, CEO of Dynamic Disc Designs Corp., developed this chair idea from the research he conducted using upright MRI in 2010 in The Spine Journal. His next step is to find a partner to bring the chair design to market to help those that suffer (and want to prevent) back pain and combat this world-wide problem.