Shape not Size
In order to more correctly understand how Office Seating must adapt for the future we need to have a better understanding of the additional factors that will change our self-reflected view of our body shapes and work requirements. Ergonomic Seating already looks at how to provide functional adjustments for people of heights and limb lengths a standard deviation away from the average, but when it comes to fitting a chair to an individual there are more combinations to consider.
Body Shape and BMI
Since 1850 it has commonly been proposed that a person’s health and general body structure could be assessed by comparing their weight in accordance with their height – the Body Mass Index or BMI. Many recent surveys and scientific studies have criticised this generalist measure. In particular much research in the 21st Century has tried to establish whether or not there are new body shapes that we should be referencing instead of just tall or short, fat or thin. The fashion industry was quick to latch on to the possibilities of new types of statistical measurement using 3-D technology resulting in a plethora of new size terminology – pear, apple, diamond, hour-glass, ad infinitum. Note that the imagery in Figure 1 is a stereotypical indicator suggesting that people might be obese or underweight proportionately in all body areas. The reality is often a combination of body section shapes.
Ever since Leonardo da Vinci’s sketch of the Vitruvian man, anthropometric measurements have indicated that average body proportions are common. In real life there are a wide range of proportions – long legs with short torsos, short legs with long torsos, wide or thin hips etc.; much more variation than can be determined through a small sample and a normal distribution.
Gender and Body Volume Distribution
Research has indicated that long periods of sitting affect women differently from men. For women in sedentary office-based occupations body volume gravitates towards the buttocks and thighs. For men, body volume builds up more at the front of the body.
In the general population, other research has corroborated that this body volume displacement has a distinct impact on the depth of fleshy support that pear-shaped women experience when they are sitting. It is believed that the fat cells in this part of the body become more dense and supportive and that this body volume acquisition could lift their body more than 25mm higher from the seat than men of similar BMI and also affect their popliteal measurements.
Put together, both of these factors will influence or actively affect the desired position of a lumbar support, and the requirement for density and comfort of supportive seat upholstery for women in general and for larger women in particular.
Gender and Body Flexion
Several studies have implied that, due to the different nature and construction of the female hip and joints, men sit differently from women. For men it is natural to sit with legs apart and hips part-rotated. For women, sitting involves rotating the hips a little more (about 5%) pushing back into the seat and raising the position of the lumbar vertebrae. Scandinavian research has outlined that a woman’s erectus spinea contains a higher frequency of Type 1 muscle fibres, which means that they have greater endurance, but they also have greater discomfort when their joints deviate from their neutral posture. Size USA anthropometric research suggested that the lumbar position for a group of men and women is usually within a few millimetres. However the sample in this study also tells us that the males were on average 100mm taller than the females. By implication, if you were to compare a male and female of similar height the female lumbar area is situated higher when seated.
The Effects of Age
As more people continue to work into their 60’s and beyond it becomes clear that office furniture should reflect the reality that spines change shape over time due to degeneration. There is a stronger risk today of encountering more instances of the need for Back Care chairs for older users regardless of whether or not they have suffered years of previous back-care neglect. The spine naturally shrinks and becomes more stiff and shaped with age, requiring improved support.
Researchers in the US also recently discovered that body volume displacement also varies ethnically – and in particular between female ethnic groups. A study showed that Hispanic women and Black women tended to develop more fat on their thighs and buttocks, but less fat on their stomachs than caucasian women. This study was designed to support Waist Hip Ratio (WHR) analysis as an indicator of health. Whereas BMI would suggest that both groups of women would suffer similar health risks, those with higher levels of body fat around their stomachs (the caucasian group) were more likely to develop bowel diseases than those where the body volume distribution was in the anterior areas.
Of course all anthropometric studies select a sample with a wide variety of subjects in order to artificially match prescribed socio-demographic distributions in age, weight and gender. However, one has to question whether this selection is likely to be representative of an office population? By their nature office workers are more sedentary than labourers or service-industry personnel and this is known to affect their body shapes.