u can do sub-q in the back of the tricep if you can get enough fat up. You can also do it in the leg. It is good to rotate it. It isnt like you need a big chunk of fat. You just have to get it under the skin into the sub-q layer bro. I went to school with this chick that worked in a doc. office she would come over and pop me with b-12 sub-q and she said that in her office they only do it in the back of the tri.