I wouldn't intentionally relax anything at any point of any lift until the set is over.
About legdrive in benchpress. Should have always push the heels down to the ground and when you lower the bar and press up you still keep tension and maybe can push a little bit harder when you press up?
Or should you do the same thing instead that you relax the legs a second when the bar hits the chest and then you press up and also use legdrive and maybe can push harder with the legs when you relaxed them before you press up?
Sorry for my english!
I wouldn't intentionally relax anything at any point of any lift until the set is over.
I usually keep my legs solid the whole time. I coil them up a little more as the bar is going down. The only way I relax is with my arms ever so slightly. This is only when I am pausing it on the bottom though. In a TNG you wouldn't have to do that. Here is a vid from last week's benching session that sort of illustrates that. Watch my legs. http://www.youtube.com/watch?v=QMo9uCSCuI8
My first bench starts at 1:08. Let me know if you have any additional questions. :-)