1. A method of generating data output containing physiological and motion-related information, the method comprising: sensing physical activity and physiological information from a subject via a single monitoring device attached to the subject, wherein the monitoring device comprises at least one motion sensor for sensing the physical activity and at least one photoplethysmography (PPG) sensor for sensing the physiological information; and processing signals from the at least one motion sensor and signals from the at least one PPG sensor, via at least one processor, into a serial data output of physiological information and motion-related information, wherein the serial data output is configured such that a plurality of subject physiological parameters comprising subject heart rate and at least one of subject heart rate variability, subject blood gas level, subject blood flow, subject blood pulse volume, subject blood analyte levels, subject breathing rate, subject breathing volume, subject blood oxygen levels, subject blood pressure, subject VO 2 max, the 1st derivative of at least one subject blood pulse, and the 2nd derivative of at least one subject blood pulse can be extracted from the physiological information, and such that a plurality of subject physical activity parameters can be extracted from the motion-related information.