I've got an AW3, and it has a hard time tracking large swings in heart rate while I'm doing high intensity interval training. Usually, after I complete an interval that increases my heart rate, the watch will show a greyed out place holder where the heart rate should be. By the time the watch can actually display my heart rate, which sometimes takes one minute, the rate has come down substantially from its peak. I've tried using the built-in workout mode for interval training and the indoor cycling mode, and they both exhibit this inability to track peak heart rate accurately. The watch is fitted snugly to my wrist, and for activities where my heart rate is reasonably constant, the watch can track it. But for HIIT, it's pretty poor. I'm considering looking for a chest strap or other sensor that works with the AW. Does anyone have any recommendations?