mattress materials is reduced according to a constructional variant the two holder cams 9 may be inclined slightly e g by 2 u00b0 to 7 u00b0 towards the central axis of symmetry of the support element 2 so that under load they assume the vertical position according to fig2 and 3 however in the practical loading case each spring bridge will adjust itself individually dependently upon the magnitude and the angle of attack of the load see for example fig4 the two spring laths 3a and 3b of the same spring bridge may even react differently without difficulty depending upon the loading fig1 shows spring lath support 8 in its middle region comprises a groove 11 in the center of which a further holder cam 12 is disposed thanks to this measure the third spring lath 3c may be anchored underneath the two spring laths 3a and 3b to provide the spring bridge 3 with a series of further adjustment possibilities owing to the provision of this additional third spring lath 3c the hardness of the under mattress may be changed at will at any desired location however by means of a further constructional variant not only a further hardness adjustment but also a height regulation of the spring bridge 3 such as illustrated by fig6 to 9.