In Lens Studio 3.1, we introduced two new templates that allows you to add AR effects designed for the body.
Full Body Attachments: Attach objects to your body
Full Body Triggers: Trigger different effects based on your body's position
However your AR effects donot have to be directly applied to the body. Take a look at the following guides that Olha put together that shows you how you can use body tracking to add additional dancers to your videos, as well as effects that are timed to music!