engleski

The influence of the redundant moving on the pressure magnitude variation by men sitting

One of the basic characteristics of the comfortable sitting is the magnitude of the pressure with its distribution in the contact regions. The sitting pressure takes effect to the bulked muscles and long bones. Its influence trough long-time duration can cause changes in soft tissues and skeleton. It is known that magnitude variations of pressure on contacting surfaces have influence on blood circulatory system of sitting surfaces. Human body is provided for moving, but not for resting. Prolonged sitting may lead to swelling of the lower extremities, especially in constrained postures. Oedema results from increased net transcapillary filtration, exceeding removal of fluids by the lymphatics. The dominant factor promoting oedema is increased capillary hydrostatic pressure, caused by increased venous pressure. The vein pressure of the feet in a horizontal position is approximately 660 Pa, increasing to 9, 3 - 10, 6 kPa in upright position. At passive sitting, the pressure is in the order of 6 - 8 kPa, determined by the height of the blood column from the feet to the heart. When walking, the vein pressure normally decreases to 3, 3 - 4 kPa, caused by vein pump mechanisms in the lower extremities [1, 2]. Based on this knowledge, short walking breaks in office work is suggested to reduce the amount of leg/foot oedema [1]. Deep venous thrombosis (DVT) and pulmonary embolism are common complications resulting from prolonged periods of bedrest or immobilization of the limbs [3]. Today it is very present fact, that even young car-drivers who immovable sit during all day, can burden own veins very strongly and it can cause the venous thrombosis. The international diagnosis for this condition is known as the effort thrombosis. Today, the passengers who travel in plane on long-time flights are warned and learned about the possible risk of the venous thrombosis. Suhov [1] was showed in her work that a human during the sitting from the time period of 5 hours changes his position about 1000 times, that response an average once in 18 seconds. The dynamics sitting or the continuous passive motion is a new technique into the ergonomic of sitting. A lot of jobs demand continuous sitting or the standstill position of any body parts. During static measurement of sitting pressure it is noticed that even very small displacements of any human body parts cause significant pressure variation [4]. Therefore, pressure measurements depending on time were performed with the aim to assess the influence of redundant moving on static measurements. Also, the influence of redundant movements on the magnitude and distribution of sitting pressures has been determined as well as the evaluation, which movements lead to the highest variation of sitting pressure magnitude. One can conclude from the pressure shape and magnitude variation, which kind of the body motions were in fact. The recommendations based on the performed investigations can be given to better explain which kind of motions should be favoured in limited conditions to realise much better dynamic sitting. The measurements of the sitting pressure were performed on the specially developed seat with the pressure transducers in form of an indentor with diameter of 8 mm, Fig. 1. In the recent studies [1, 6] total displacements of sitting surface during the long time period were measured, free from the places where the displacements were originated. On the ground of such recorded data a Fourier frequency analysis of displacements in range of 0-20 cycles/min was performed. The measurements were performed in the area under the sitting bones (tuber ossis ischii) or near this area. The sitting pressure variation acts also as the dynamic pump that promotes the blood circulation in the vein-pumping systems. The redundant movements activate some muscle groups as agonists or as antagonists and their activities also promote the blood circulation in the vein systems.

redundant moving; human sitting; measurement; magnitude variation of pressure

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