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MEETING
ISO STANDARDS
The International Organization for Standardization (ISO) develops standards for all types of products, including wheelchair seat cushions. These standardized tests are established to evaluate how a product performs on measures that impact the user of the product. The University of Pittsburgh School of Health and Rehabilitation Sciences performed standardized bench tests on 10 office chair seat cushions to evaluate performance, considering most people sit in these seats for at least 8hrs per day. Since the population sitting in office chairs is largely not at risk of tissue injury from sitting, they focused on three known measures of comfort based on existing research: peak pressure index, contact area, and shear.
Examples of Pressure Map Readings
Biomechanical and tissue modeling performed by Simuserv integrated by Abaqus Unified FEA from Dassault Systèmes.
PRESSURE MAPPING ISO 16840-6
PEAK PRESSURE INDEX
Peak pressure implies high pressures in one area. The peak pressure index is what is calculated by averaging the individual sensor results along the simulated IT (sit bones) portion of the testing fixture. Rather than simply taking the single highest value as the peak pressure, one random reading won’t skew the results or the perception of performance. A high peak pressure index (red) is associated with discomfort or pain, so low values are desired (blue).
*Performed on 6/8/22 at the University of Pittsburgh with a rigid load indenter. Human results may vary.
ANTHROS CHAIR
SECRETLAB TITAN
HERMAN MILLER EMBODY
HERMAN MILLER AERON
PRESSURE MAPPING ISO 16840-6
CONTACT AREA
A measure that shows how well the force from the body is being managed by the seat cushion. A comfortable seat cushion should be designed to have the greatest pressure distribution or contact area possible. Higher values are desirable and indicate greater contact between the indenter and the cushion.
HORIZONTAL STIFFNESS ISO 16840-2
SLIDE RESISTANCE + SHEAR FORCE
Slide resistance indicates how easy it is to slide forward in the seat. A comfortable seat will have enough resistance to keep the pelvis in place. A high slide resistance value is desirable. While there needs to be enough resistance to stay back in the chair, the goal is to minimize tugging of the tissues at the sit bones. So, in addition to the horizontal stiffness ISO test, an additional shear force test can give us this information.
Shear is the combination of downward pressure (in sitting, through the buttocks), and horizontal friction (sliding forward in your seat when your skin sticks to the seat and you feel that pull). It may be described as the feeling of sliding out or forwards” on an office chair. The strain on your tissues from that friction can be painful and cause discomfort. A low shear value is desirable.
THE RESULTS SPEAK FOR THEMSELVES
Anthros outperformed the leading office and gaming chairs in the world
Up to
%Decreased seat pressure
Up to
%Decreased sliding
Up to
%More contact area
SIT STUDY
LEADERBOARD
| RANK | CHAIR | LOWEST PRESSURE
PEAK PRESSURE INDEXPeak pressure implies high pressures in one area. The peak pressure index is what is calculated by averaging the individual sensor results along the simulated IT (sit bones) portion of the testing fixture. Rather than simply taking the single highest value as the peak pressure, one random reading won’t skew the results or the perception of performance. |
LOWEST SHEAR
SHEARShear is the combination of downward pressure (in sitting, through the buttocks), and horizontal friction (sliding forward in your seat when your skin sticks to the seat and you feel that pull). Imagine a child sliding down a metal slide wearing a bathing suit, with skin sticking to the slide all the way down; this is shear. |
HIGHEST CONTACT AREA
CONTACT AREAContact area represents how much contact the indenter (or person) is making with the seat surface. A higher contact area is desired as it implies greater pressure distribution and lower peak pressures. |
|---|---|---|---|---|
| 1 | Anthros | 67 | 7 | 100,342 |
| 2 | Steelcase Leap | 101.7 | 10.5 | 82,267 |
| 3 | Humanscale Freedom | 94.5 | 13 | 77,241 |
| 4 | Steelcase Gesture | 115 | 12.9 | 80,282 |
| 5 | X-chair | 127.55 | 16 | 66,515 |
| 6 | Maxnomic | 108.6 | 21.2 | 58,997 |
| 7 | Herman Miller Embody | 168.2 | 16.1 | 55,070 |
| 8 | SecretLab | 166.4 | 17.1 | 51,649 |
| 9 | Herman Miller Aeron | 183.6 | 23 | 41,767 |
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