(FINAL)
Another tool I do like is the cat o'nine tails whip or a scourge whip. I prefer they are heavy rough leather, and studded at the ends of each leather strip with spiked or heavy ball bearing type studs (enough to bruise the skin and underlying muscle, or tear the skin if used long enough on the victim).
Having the victim restrained and hung by their wrists, so that their weight works to strain the muscles. I do like the idea of attaching weighted nipple clamps as well.
Piercing or branding also works for me.
I'm sure there are other tools I'd like to use.