An S-Track massage chair's rollers follow the curvature of your spine and stop at the base/bottom of your spine. S-Track chairs typically top out at 32" long. Until recently, most 3D massage chairs were S-Track. In fact, many Asians prefer an S-Track roller and don't trust L-Tracks as much.
An L-Track massage chair's rollers are much longer and will follow the curvature of your spine and then round the glutes often massaging to the top of your hamstrings. The longest L-Track available in the market today is the Luraco Legend with a 58" L-track while most are in the 50-53" range. Until 2017, there were no 3D L-track massage chairs available. Now, there are many options if you're looking for a deeper tissue 3D massage that not only hits your back, but also your glutes and hamstrings. We've now even seen a couple of 4D L-Track chairs find their way into the marketing in 2018.