is attached to one side of the rigid backrest frame 21 by fixed straps 31 opposite the adjustable tension member 51 are a pair of guide members 33 as shown in fig2 the cable runs from the adjustable tension mechanism to the first guide member 33 attached to the first side of the rigid backrest frame 21 around the cable guide 55 on the adjustable tension member 51 and then around the second guide member 33 attached to the first side of the frame and then back to the adjustable tension mechanism preferably and as shown in fig1 the front of the backrest 11 is covered by a cover 61 that may or may not include additional cushioning additional lateral supports not shown attachable to the backrest for further positioning needs fig5 shows two additional embodiments of the claimed invention specifically fig5 shows five 5 adjustable support structures 45 the upper two 2 adjustable support structures 45 are identical to those disclosed elsewhere in this detailed description the lower two 2 support structures 45 while similar in function are slightly different in appearance specifically instead of a cable 41 that stretches across the backrest 11 to the opposite side of the backrest flat straps 83 are tensioned across backrest using an adjustable tension member.