Heat Pad / Rice Sack ETC

Hi I was interested in checking what technique the PE’rs out there for warm up / Down for PE.
Yes I have seen the video, however the method shown was applying heat on the belly pad and to my understanding this would be indirect heating yes?
My reason for asking is two fold, firstly I use a rice/wheat sock zapped in the micro for 2:22 minutes and wrap around the length of bone for five minutes do the exercises and afterwards bag it again. Obviously this heats the bone.
What is your method?

Also. I have seen USB or mains powered heat pads on evilbay. Has any one had any experience with these items?