I know the general consensus is to focus on the one hand going forward and up quickly on the start. Does anybody ever concentrate on the other hand by extending it the all the way back? I noticed asafa does this when he starts.
I think my shoulder would dislocate if I brought it back as far as Asafa Powell. 
I haven’t looked at this, but I will! When I used to start with Darren, I noticed his rear elbow remained very bent, not well termed I know! This seems opposite to the cue you’re suggesting.
Does anybody ever concentrate on the other hand by extending it the all the way back?
I do. For me it’s proven to be a way more effective cue to focus on than lifting my left, forward swinging arm. My left arm goes high and above my head - whether I think about it or not - so it’s not really an issue.
I know Charlie is an advocate of concentrating on the forward moving arm, so I suppose it’s whatever you find yields the best and most consistent results.
I’ve been trying it the last while and I like the results… so i think I’ll stick with it.
the reason that most need to concentrate on the lead hand forward is that there is seldom a problem with the other hand going back. If there is, of course, you’ll need to work there too.
would it not help you out in the start if your hand was in the back and then drove it forward with your opposite leg and possibly increase your initial burst off the start?
the rules state that if you are in the blocks, both hands must be in contact with the track.