The OS-4000 Zero Gravity massage chair is ergonomically designed to
contour a variety of spine shapes. The Spine curvature is unique from
one individual to the next. The S-track system allows the roller heads
to massage along the back from the neck down to the lower spine with a
consistent pressure in the massage, along with a comfortable support.
The typical massage tracks, being linear, create an inconsistency in
pressure applying weak massages in the neck and lower back.