How do wrist-worn health trackers estimate VO2 max without a chest strap?

13 Eki 14:00

I'm trying to understand how wrist‑worn health devices calculate VO2 max using just optical sensors and motion data. They claim to provide a decent estimate without any external equipment. What kind of algorithms or physiological models are typically employed, and how reliable are these numbers compared to lab measurements? Also, does the accuracy vary significantly with factors like skin tone or wrist placement? Would love to hear explanations or resources on the underlying science.