Sitting pressure distribution for different chair types

Reijo Koskelo, FT, Researcher, Kuopio University, 2010, ABSTRACT

Introduction

Complaints related to supportive and locomotive areas of the body are one of the main reasons for sickness from work. Neck and back pains especially have increased to a remarkable level to prevent sufferers from being able to work. In the future more attention should be paid to the impact of ergonomic seating in regard to the overall health levels of individuals. Traditional seating positions result in the delivery of large scale pressure levels over the thighs, buttocks and genitals which weakens the circulation in soft tissues and the legs. Pressure that is levelled predominantly over the area of the genitals also squeezes the inner pudendal arteries, which take care of the blood supply for erectile tissue, both in terms of normal blood flow and erections. For male bicycle riders, blood circulation weakens due to the saddle exerting pressure over the pudendal arteries and long term pressure on the arteries causes a thickening of the arterial wall and subsequent erection disorders (V Huang, R Munarriz & I Goldstein, 2005). The target of this study was to investigate the different pressure levels caused by eight different chairs, and the distribution of this pressure between the thighs, buttocks and genitals. 

Methods

Nine volunteers participated in the study (five women and four men). The average age of the subjects was 32 years and the age range remained between 21–55 years. Before any pressure measurements took place, the knee and hip angle for each test subject was fixed in such a manner that it remained at an angle of 135 degrees for each of the different saddle chairs. Studies have shown that an angle of 135 degrees is the most suitable when taking into account the need to maintain a healthy back (W. Bashir 2006). On the traditional office chair the angle was set at 90 or 110 degrees, which made it possible for their feet to be placed on the floor. The sitting angle for all test subjects was fixed in three ways.

Each test subject’s eyes were covered so that they would not be able to see which particular chair they were sitting on at any moment. They also couldn’t see the different chairs that were being used for the study beforehand.

The chair models being used for the study were as follows:
A) Triton Activ office chair with a back rest (Martela Oy, Finland)
B) HÅG Capisco saddle chair with a back rest (HÅG/RH/RBM Group, Norway)
C) Bambach Saddle Seat saddle chair (Bambach Saddle Seat™, Australia)
D) BackApp saddle-like chair (Back App Europe AB, Norway)
E) Salli Classic saddle chair (Easydoing Oy, Finland)
F) Ponychair® saddle chair (MJ Paasikivi Oy, Finland)
G) Salli Twin saddle chair (Easydoing Oy, Finland)
H) Perfect Saddle saddle chair (Support Design AB, Sweden)

Seating pressure levels were measured by the Tekscan pressure mat (Tekscan Advanced ClinSeat DB, v.5.64C, Tekscan Inc, Boston MA, USA) during 20 seconds.

Results

In the measurement of seating pressure levels, the smallest pressure area was found when the subject was sitting on Chair G (the Salli Twin) for all test subjects. On Chair A (the Triton Activ), the thighs and buttocks were subjected to the highest pressure levels. By comparing those areas that were subjected to pressure it was found that in case of Chairs E (the Salli Classic) and G (the Salli Twin) the pressure was clearly and almost completely targeted on the area of the ischium (sitting bones). With the other chair models in the study, seating pressure was divided over a larger part of the test subject’s seated areas and on their thigh muscles. Seating pressure was also especially notable around the area of the genitals, and Chair D (the Back App) had it most. For all test subjects, pressure levels around the genitals whilst seated on the split-seat saddle chair, Salli Twin, were the lowest when compared to the other chair models.

The table shows the area of highest pressure for each test subject on each chair. The pressure areas were divided into five: thigh muscle (R), musculus glutaeus (P), seat nodes (I), pelvic diaphragm (L) and genital area (G). Area I is the most advantageous considering blood circulation, metabolism and nerve endings.

koskelo_tuolit.jpg

koskelo_paineet.jpg

Table 1 shows the area of highest pressure for each test subject on each chair. The pressure areas were divided into five: thigh muscle (R), musculus glutaeus (P), seat nodes (I), pelvic diaphragm (L) and genital area (G). Area I is the most advantageous considering blood circulation, metabolism and nerve endings.

Test person Triton Active HÅG Capisco Bambach Saddle Seat BackApp Salli Classic Ponychair Salli Twin Perfect Saddle
1 R, P   L G     I  
2 R, P     G     I L
3 R, P     P L, G   I  
4 R, P   G       I L
5 R P   G L   I  
6 R P   G     I L
7 R P   G L   I  
8 R   G L P   I  
9 R, P     L, G     I  

Conclusions

Seating pressure caused by different chairs, plus the ergonomics and usability of such chairs, is something that has not been researched much as of today. Considering the improvements that have been made in seating ergonomics and seating health, it is of the utmost importance that research continues on the impact of long-term seating in regard to the health of individuals and their feeling up to being able to work.

Of the chairs that were included in the research, the split-seat and height-declination adjustable Salli Twin places seating pressure over the smallest area of the body. Pressure is not aimed over the pectineal line or the genitals, so that blood circulation in tissues and the metabolism in the relevant areas remain active. The seating position is naturally straight and individuals’ legs do not go numb even while they have been seated for longer periods of time.