Hi, I'm planning a study where I will monitor ~ 30 individuals over several months using apple bell, and compare respiratory / heart rate related signals with medical imaging such as ultrasound, dense ECG and heart MR.  Since I'm still waiting for my Apple Watch to come, I have some questions:
I wonder if it's possible to continuously record heart rate using Apple Watch all day or if this is too demanding on the battery ? is heart rate accurate during movement, does it stick properly to the wrist to monitor the pulse accurately during spontaneous movement, or do you need to stop moving to measure it?
I also wonder if it is possible to hack the apple clock to create my own apps to access pulse / ECG, and save the recording / upload them automatically to the cloud? It would make data collection much easier.
Are there other physiological sensors in addition to ECG / pulse that I should be aware of? I would like to deduce as much from the clock recordings as possible.