I haven't found a wrist based HR sensor yet that could keep up with rapid change interval training. I currently use a Scosche rhythym band that works decently, but not perfectly. Seems like the only solution is a chest band, which I would much rather not wear. At the other end of the spectrum is the junk on the Android side where the watch actually tells you to stand still, then takes several seconds to get a reading, totally unacceptable for an athlete. Which end of the spectrum does the AW series 2 lie? Is the HR fast, is it accurate, does it make you stand still, and will it keep up with interval training?