friction reduction plates 80 81 or otherwise enhancing use alternatively a variable friction device or weights are usable so as to provide resistance with respect to movement of movement blocks 70 71 friction reduction plates 80 81 are attached to the swivel plates 50 51 beneath the movement rods 60 61 and beneath the movement blocks 70 71 in one embodiment the friction reduction plates 80 81 have coatings applied that reduce the friction between the plates 80 81 and the movement blocks 70 71 one such type of coating is teflon u00ae made by dupont e i de nemours amp co of wilmington del movement stops 95 96 are attached to the movement rods 60 61 the movement stops 95 96 are adjustable to any point along the movement rods 60 61 and securable at any position along the rods 60 61 the movement stops 95 96 prevents the movement blocks 70 71 from being moved beyond the movement stops 95 96 in one embodiment each movement stop 95 96 has a rubber like coating on the side against which the movement block 70 71 respectively touches during usage alternatively a rubber like washer is placeable around each movement rod 60 61 in front of the movement stops 95 96 and in front of the attachment bars 92 93 one advantage of the rubber like coating or rubber like washer is muffling or other reduction in the sound produced when the movement blocks 70 71 encounter the movement stops 95 96 and.