Massage chair buying guide: 3D vs 4D, S and SL tracks, and zero gravity

What the rail changes

The track is the path the main roller carriage follows. An S-shaped track typically follows the back; an L or SL track often continues below the seat toward the glutes. Ask for a coverage diagram and compare the first and last contact points on a person of your height. A longer rail does not tell you where the rollers make useful contact.

What 3D and 4D change

Brands commonly use 3D for rollers that can extend toward the body or retract, and 4D for systems that also vary speed or rhythm. Confirm how the specific model implements these controls. Ask the seller to show the gentlest and strongest depths and whether you can change speed and depth separately in manual mode.

Zero gravity and room fit

Zero gravity is a reclining posture that raises the legs relative to the upright position. Look up the actual dimensions with the back reclined and the footrest extended. Mark both the rear clearance and the forward sweep on the floor; a wall-saving base can still require space in front.

Run the same short trial

On each chair, use the same light setting and compare shoulder contact after the scan, lower-back contact, and where the footrest meets your heels. Adjust the shoulders manually if possible. If two people will use the chair, both should test whether they can enter, exit and reach the stop control comfortably.

What to request in writing

Ask for the model number, fit range, clearances, available controls and parts coverage on one spec sheet. For examples of how manufacturers describe these functions, see Osaki’s buyer guide and Fujiiryoki’s track guide.