A system for simultaneous monitoring of a plurality of individuals including an individual physiological data logger (IPDL) for each individual for measuring and storing heart beat data, the IPDL including: an electro-cardiogram (ECG) measuring device for providing heart beat data, an extended memory for storing the measured heart beat data, a synchronization element, a micro-controller including a synchronization element controlling circuit, and RF transceiver apparatus; a central interface unit selectably couplable by radio telemetry communication to each IPDL for transmitting thereto a plurality of commands and for receiving therefrom the heart beat data; and a computer coupled to the central interface unit for providing commands for each IPDL, for performance of an individual bench test for deriving a conversion coefficient of heart beat cost per unit of mechanical work, and for monitoring and analyzing, in real time, the heart beat data of each of the plurality of individuals.