So the one big disappointment I've had so far with the Apple Watch is definitely weightlifting. The HRM always loses my heartbeat during a lifting session and it fluctuates between 55 bpm and 160 bpm. I know that my heartbeat never dropped below 120 though while I'm lifting weights. Does anybody else have this problem? Or should I take my watch back and get an exchange. Here's a picture of the fluctuations.