When you train back, how many sets do you do? To me, that would have a part in how often you train back.

Myself, I train back once a week but do 17 to 18 sets over 5 different exercises. IMHO, at least for me, 17 to 18 sets of back twice a week would be too much.

Like biggin said, won't hurt to give it a try and see how it goes.

JMO....