"Strict" in what sense? If you go really slow on them, it is quite hard to get to failure, as just holding it there at the bottom for even a few seconds, allows for SOME recovery to occur(imo). When I do them(and I just started to do them again), I pause at the top, but come down quick, and right back up. NO PAUSE at the bottom whatsoever. This allows my back muscles to fail FIRST, WITHOUT allowing the biceps or the back time to recoup. If that makes any sense. So if you are going slow on them(well, at least for me), and ESPECIALLY if you are pausing for a stretch at the bottom, you(I) will cheat yourself out of obtaining BACK MUSCLE failure, faster.