fig1 shows a deformable region 22 of the support surface 3 in the retracted position of the support surface 3 . in the position shown in fig1 , telescopic rods 1 of the telescopic mechanism are completely inserted in telescopic sleeves 2 provided in the frame of the telescopic mechanism . the support surface 3 is displaced into its retracted position to accommodate a short person . the displacement of the telescopic rods 1 , together with the support surface 3 secured thereto , is effected by a height controlling mechanism including tooth bars 4 which are attached to the support surface 3 , and tooth gears 5 which cooperate with respective bars 4 and which are supported on a common shaft supported in brackets 7 secured to respective sleeves 2 . the displacement of the support surface 3 is effected manually with a hand wheel 6 . the support surface 3 can be displaced in any position between the completely retracted position shown in fig1 , and a completely pull - out position shown in fig2 in which the deformable region is completely expanded as shown with a reference numeral 23 . fig1 a and 2 a show , respectively , views similar to those of fig1 and 2 and showing telescopic rods of the telescopic mechanism being surrounded by sliding elements 8 which are secured to respective telescopic sleeves 2 by brackets 29 , as shown in fig1 a . as further shown in fig1 a , the sliding elements 8 almost completely surround the telescopic rods 1 in the retracted position of the deformable region 22 of the support surface 3 . however , the sliding elements 8 , as shown in fig2 a , only partially surround the telescopic rods in the pull - out position of the deformable region 22 of the support surface 3 . fig3 shows the support frame 30 for the support surface 3 , together with the height controlling mechanism . fig4 shows the support frame 30 shown in fig3 but with means for relaxation of thigh muscles . the relaxation means includes a support 12 and a resilient strip 14 mounted on the support 12 and having a smooth surface 13 . fig5 shows a cross - sectional view of the telescopic rods 1 and the support surface 3 which is attached to the slide connection elements 8 surrounding the telescopic rods 1 and secured thereto . means 9 provides for stretching of the support surface 3 . the reference manual 9 represent a back cover which can be more elastic or less elastic . the support surface can be formed of upholstery 10 of textile or foam material which is covered by a covering 11 . fig6 shows a folding mechanism 15 which controls the position of the telescopic sleeve 2 . the telescopic sleeve 2 is retained in its predetermined position by an axle bolt 17 displaceable in a slot 16 . fig7 shows the position of the folding mechanism 15 in a maximum extended position of the sleeve 2 . fig8 and 9 show the mechanism for displacing the telescopic rods 1 between their retracted ( fig8 ) and pull - out ( fig9 ) positions which correspond , respectively , to folded and extended positions of the telescopic sleeves 2 which are determined by positions of the axle bolt 17 in the slot 16 . the axle bolt 17 is displaced by displacement bars 18 which is displaced by a lever mechanism including two levers 19 . the free ends of the levers 19 are connected with the telescopic rods 1 by displacement bars 20 . upon appropriate actuation of the lever mechanism , the telescopic sleeves 2 and the telescopic rods ii are displaced from the retracted position shown in fig8 to the pull - out position shown in fig9 . fig1 shows an end element 21 with which a synchronized displacement of the telescopic rods 1 is achieved . the end element 21 is attached to a region 25 of the support surface 3 the length of which does not change during displacement of telescopic rods 1 between the retraced and pullout positions . with the constant length region 25 , a height - controlling mechanism for displacing the telescopic rods 1 is not necessary . the retraction and pull - out is effected by a corresponding displacement of the cover 9 in a respective direction for displacing the telescopic rods 1 in the channels 26 . the end element 21 is connected to the bending region 25 in a predetermined spaced relationship with respect to the corresponding telescopic sleeves 2 . the angular position of the deformable end element 21 influences the position of the telescopic rods 1 . the different positions of the telescopic rods 1 correspond to different degrees of deformation of the end element 21 which is supported at its opposite ends in brackets 29 ( fig1 ). the position of the telescopic rods 1 depend on the degree of stiffness of the deformed end element 21 . thus , the changing of the angular position or the degree of deformation of the end element 21 results in a desired displacement of the telescopic rods 1 . this permits to eliminate the height controlling mechanism . different degrees of deformation of the end element 21 are shown in fig1 – 15 . the reference numeral 27 and 28 show the positions of telescopic rods 1 in the retracted ( fig1 ) and pull - out ( fig1 ) positions . reference numerals 27 a , 28 a designate conditions of the coverings of the telescopic rods 1 . the present invention makes a substantial contribution to the advancement of health care . the present invention is based on an effective use of ecological resources . the present invention is based on a mechanical principle that contributes to economy of material and sets forth alternative possibilities of changing the conditions of the support surface without the use of external energy sources . though the present invention was shown and described with references to the preferred embodiments , such are merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art . it is therefore not intended that the present invention be limited to the disclosed embodiments or details thereof , and the present invention includes all variations and / or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims .