Combination of a waistrest and a backrest

A combination of a waistrest and a backrest comprising:

• a front frame that is annular and made of rigid material, with the front frame including a central hollow portion having two lateral sides, with two flexible plates provided on the two lateral sides of the central hollow portion of the front frame, with each of the two flexible plates including a plurality of positioning members spaced in a vertical direction, with a positioning groove defined between two adjacent positioning members, with the front frame covered by a net, with the net providing support for a user leaning against the backrest by spanning the central hollow portion of the front frame;
• a rear frame that is annular and made of rigid material, with the rear frame engaged with the front frame, with the rear frame including a central hollow portion having two lateral sides, with a guiding groove defined in each of the two lateral sides of the central hollow portion of the rear frame and extending in the vertical direction, with each of the guiding grooves including a front opening and upper and lower ends, with upper and lower stops respectively formed on the upper and lower ends of each of the guiding grooves;
• and
• a waistrest including a support portion having two sides, with a lug formed on each of the two sides of the support portion, with each of the lugs including a front face and a rear face, with a protrusion formed on the rear face of each of the lugs, with the protrusion of each of the lugs received in one of the guiding grooves of the rear frame and limited by the upper and lower stops, with a first positioning member formed on the front face of each of the lugs, with each of the flexible plates abutting the front face of one of the lugs of the waistrest, with the first positioning member of each of the lugs of the waistrest engaged in one of the positioning grooves of one of the flexible plates.