You answer:

Manufacturers typically opt for an S or L-Track massage system, which refers to the way the massage nodes move up and down your back (in either an S or an L shape essentially).

However amazingly you get the option of both directions on this model, giving your back the best coverage it could ask for!

You still get plenty of other features too, like six massage modes including a full body airbag massage and lower back heat function.
https://techypes.com/best-massage-chairs/