If you are suffering from osteopenia or osteoporosis, a spiral, linear or tri-planar machine is best for you. Linear machines go straight up and down. They are very effective in building muscle, but they are also a bit more jarring on the body. Tri-planar machines are the update to linear machines--they are very effective at building muscle, but without the rough movements on the body. This platform does go up and down, but it also goes front to back, so it's a much more fluid motion. Spiral machines have two totally different motions--Triplanar (up-down/front-back) and Pivotal (see-saw) that can be used independently or together. When used together, these two motors make a figure 8 motion. This is an extremely gentle motion on the gel areas of the spine and joints, with many benefits such as lymphatic drainage, improved circulation, improved bone density, pain reduction, detoxification and muscle building on the higher hertz ranges.