This is the tool to make massage for the deep muscles of backbone. The size of model is designed for the children first. For adults use scaling factor 1.2 - 1.3.
Print the model legs up. Brim is activated to hold the model better.
When model is printed polish the balls with sandpaper 240 and then heat the balls up with the heating fan (very carefully, to melt only surface and avoid full melting, keep the model in the fridge couple of hours in advance). This will make the balls fine and make it friendly for the skin.

RepRap

Prusa I3

No

No

0.15

30

My recommendation is to use 3 mm walls thickness and 30% infill rate. I have printed two models and it is strong enough even for really high pressure.

Designed using Materialize magic