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Statements of medical professionals about the Koskelo study


Distribution of sitting pressure in the genital and the buttocks-thigh area, when sitting on different types of saddle chairs

Reijo Koskelo
PhD, Master of Health Sciences, Scientist
26 September 2008

Introduction

It is known that the distribution of sitting pressure in the human body varies significantly depending on the seat. However, there are no available reference values on pressure that is harmful to human beings. Because of the lack of reference values, the harmfulness is only determined based on the subjective experience of a sitting person and his/her feeling of discomfort. Sitting pressure has an effect on the sitting position of a human being as he/she tries to avoid unpleasant pressure. The seat can be designed in such a way that the natural sitting position causes as little pressure as possible.
 
Several studies have demonstrated that male competitive cyclists have genital disorders because of the pressure caused by a solid bicycle saddle and subjected to the base of the penis. There are reasons to believe that these disorders may also occur when spending a prolonged time sitting on a saddle chair with a solid seat at work.

When sitting on a regular chair, the pelvis is subjected to pressure, which causes generally known numbness of soft tissues in the buttocks and at the back of thighs, if the pressure lasts for a long time. Sitting on sitting bones on a saddle chair causes less numbness. This may lead to the conclusion that men who sit on a regular chair usually subconsciously lean their pelvis backwards in order to avoid causing pressure in the sensitive genital area. When sitting on non-divided saddle chairs, the base of the penis is subjected to easily noticeable and unpleasant pressure, which may also cause erectile dysfunctions under certain conditions. On a two-part saddle chair, there is no such pressure.

Panty liners, tight underwear and prolonged sitting may increase the temperature and humidity of the female genital area because of poor ventilation. When sitting on a divided saddle chair, the genital area is on the gap and gets more air and obviously is better ventilated, which may decrease the infection risk.

When the thighs were 45 degrees bent downwards, measured from a horizontal level, most of the test persons had the pelvis in a similar upright position as when they were standing, while the back was in a natural S-position (lordosis) and the upper back arch (kyphosis) without active work of the back or hip muscles.

Methods

The target of the study was to investigate three different types of saddle chairs (Salli MultiAdjuster, Salli Classic and Bambach) in order to compare the strength of the pressure that these chairs cause, and the distribution of this pressure between the thighs, buttocks and genitals.

Salli MultiAdjuster (manufacturer Salli Systems, Finland)
- height adjustment with a gas cylinder
- inclination and width adjustment
- total weight of the chair 13 kg
- two-part seat, the width of the seat is adjustable
 
 
 

Salli Classic (manufacturer Salli Systems, Finland)
- height adjustment with a gas cylinder
- inclination adjustment
- total weight of the chair 12 kg
- solid seat
 
 
 

Bambach Chair (manufacturer Bambach Saddle Seat, Australia)
- height adjustment with a gas cylinder
- inclination adjustment
- total weight of the chair 7.8 kg
- solid seat
 
 
 
 
During the measurements, all the test persons had the chair declination adjusted to the middle position. The height of the chair was adjusted according to the height of each test person.

The test persons sat in a similar position on each chair with a thigh angle of 90 degrees and the lordosis angle was made as identical for each test person as possible. The position of the test persons was regulated with the aid of an angle measuring device (thigh angle) and a citrometer (lordosis).

Test persons

Ten voluntary, healthy persons – five women and five men – participated in the measurements.
The test persons were aged between 20 and 60 years of age.
The average height of the women was 166.4 cm and average weight 55.8 kg.
The average height of men was 175 cm and average weight 79.2 kg.

Table 1. The height and weight of the test persons n=10 (women 1–5, men 6–10)
 
 
Test person number Height cm Weight kg
1 164 52
2 164 56
3 167 58
4 175 63
5 162 50
6 173 80
7 176 78
8 170 78
9 170 73
10 186 87


Measuring instrument

The rating system used in the subjective (test person’s feeling) questionnaire was on a 0–10 scale, where (0) was defined as the worst possible feeling and (10) as the best possible feeling.

The sitting pressure was measured by using a Tekscan Pressure Measuring Mat (manufacturer Tekscan Inc., USA), which measured the distribution of the test person’s sitting pressure to the genital and the buttocks-thigh area.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Results
 
Table 2. The test persons’ n=10 (women 1–5, men 6–10) subjective evaluation of the sitting experience related to Bambach, Salli Classic and Salli MultiAdjuster chairs.
 
 
Test person number Bambach Salli Classic Salli Multiadjuster
1 4 8 9
2 1 5 9.5
3 8 9 7
4 5 6 9
5 5 7 9
6 1 7 9
7 4 5 9
8 6 7 9
9 7 7 9
10 2 5 8


The subjective evaluations of the test persons (0-10):

Women (average): Salli MultiAdjuster 8.7, Salli Classic 7.0, Bambach 4.6
Men (average): Salli MultiAdjuster 8.8, Salli Classic 6.2, Bambach 4.0

Based on their subjective sitting experience, the women (8.7) and the men (8.8) clearly ranked the Salli MultiAdjuster as the best chair model. The Salli Classic was ranked as the second best chair (women 7.0, men 6.2). The Bambach chair was ranked as the worst chair by the test persons (women 4.6, men 4.0).

Comparing the pressure strength in the genital and the buttocks-thigh area

The seats of the chairs, which were measured, were almost of the same size.
 
The Salli MultiAdjuster has a two-parted seat. There was no pressure measured in the genital area and only a little pressure in the back part of the thighs. The pressure was only distributed to the ischial bones.

The Salli Classic has a solid, one-parted seat. The genital area and the ischial bones were subjected to pressure, and there was a little pressure on the back part of the thighs.

The seat pressure of the Bambach chair was subjected to the genital area and to the back part of the thighs.

Conclusions

In the research introduction event, before the questionnaires were filled in, it was made sure that the test persons understood how to fill in the forms. The test persons filled in a self-evaluation form after the measurement of each chair and marked the information as subjective.

The Bambach saddle chair was ranked the most uncomfortable by the test persons. On that chair, the pressure was strongly subjected to the genital area and to the thighs.

When sitting on a Salli Classic chair, the pressure subjected to the thighs was lower than on the Bambach chair but the pressure subjected to the male pubic bone area was higher than on the Salli MultiAdjuster chair and it caused some discomfort. The Salli Classic probably suits women better than men because of the anatomical difference in the female and male genital areas.

According to the results of this study, the test persons found the Salli MultiAdjuster chair to be the most comfortable for sitting. When sitting on a Salli MultiAdjuster chair, with a two-parted seat, the pressure subjected to the genitals is low or negligible and was mostly caused by tight clothes as a result of the sitting position tensions. According to the measured pressures, the blood circulation in the lower parts of the hips and the nerve functions are least disturbed when sitting on this chair model. Also, the pressure subjected to the area of the back part of the thigh was less than with the Salli Classic and Bambach chairs. It seems that sitting on a two-part saddle chair enables one to maintain the thigh angle of about 45 degrees downwards from the horizontal level without pressure on the genital area and with the back in good and natural posture.

The temperature of the male testicles may increase to 37 degrees when sitting on a conventional chair. Accordingly, sitting on a saddle chair cools down the testicles to their optimal temperature of 33–34 degrees (Reijo Koskelo, Osmo Hänninen, The University of Kuopio, 1999). The middle gap of a divided seat probably increases the important ventilation of the genital area and promotes genital health.

When sitting on a saddle chair, which has a solid seat, the base of the penis is subjected to pressure, which can disrupt or damage the nerves and blood vessels in the area. During the past eighteen years, fourteen studies have been made among cyclists, concerning the pressure subjected to the penis and its connection to erectile dysfunctions. The results have shown that cycling more than three hours a week causes a significant risk of getting erectile dysfunctions (References 2–4).

Regarding women, a long time spent sitting on a saddle chair with a solid seat may increase the humidity and temperature of the genital area and that way also the infection risk. When sitting on a Salli MultiAdjuster chair with a divided seat, the genital area gets ventilated and the infection risk may decrease.

Sitting on a divided saddle seat enables the hips to be declined forwards without subjecting  the pubic bones or genitals to pressure. This facilitates the natural lordosis of the back during the sitting.

In conclusion, sitting on a Salli MultiAdjuster chair with a divided seat, compared with the other two saddle chair models, best enables the pelvis to be declined forwards without subjecting the pubic bones or genitals to pressure. This makes it easy to maintain the natural lordosis of the back and back posture, while sitting in a natural position.
 
Literature references
  1. Reijo Koskelo, Osmo Hänninen. The effect of different seats on testicular temperature. The University of Kuopio, 1999
  2. Ricardo Munarriz, Vincent Huang, Jayant Uberoi, Scott Maitland, Terry Payton, Irwin Goldstein. Only the Nose Knows: Penile Hemodynamic Study of the Perineum - Saddle Interface in Men with Erectile Dysfunction Utilising Bicycle Saddles and Seats with and without Nose Extensions. Institute for Sexual Medicine, Boston University, J Sex Med 2005
  3. Vincent Huang, Ricardo Munarriz, Irwin Goldstein. Bicycle Riding and Erectile Dysfunction: An Increase in Interest (and Concern). Institute for Sexual Medicine, Boston University, J Sex Med 2005

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