Physiological monitoring devices and methods using optical sensors

A monitoring device configured to be attached to a subject, the monitoring device comprising:

• a photoplethysmography (PPG) sensor configured to measure physiological information from the subject;
• at least one motion sensor configured to detect an activity state of the subject;
• a blood flow stimulator;
• and
• at least one processor configured to process signals from the at least one motion sensor to determine an activity state of the subject, and wherein, in response to an activity state determination, the at least one processor is configured to instruct the blood flow stimulator to increase blood perfusion at a location where the PPG sensor is attached to the subject.