Its very simple on Zbrush.
1 - Sculp your model, its a good point start with Z-Spheres.
2 - Mask detailed areas
3 - Use Decimate Master to triangulate body and torso with extremely low poly options.
4 - Invert mask
5 - Decimate the other parts with a less aggressive decimate master options.
6 - Merge and Weld.
Before export in 3Ds MAx, add a smoth layer, and dont click in nothing.
Any kind of already mesh can be processed with this technique.
Here is a Blender tutorial, i just adapted the concepts for my software.