NOVELTY - The light sensor has a circular support member engageable circumferentially with a body part of a person; light emitters (21,22,23) located about a circumference of the circular support member for emitting light signals into different areas of tissue surrounding the body part; and light detectors (24,25,26) located about a circumference of the circular support member for receiving reflected light signals from the different areas of tissue surrounding the body part.    USE - Noninvasive light sensor for monitoring body parameters of a wearer during exercise, e.g. for detecting heart beat signals.    ADVANTAGE - Enables playback of the audio/video files stored on the device. Determines and displays the instantaneous heart rate and stores a heart rate profile during an exercise period. Stores and displays the number of steps taken. Determines, displays and stores the health related status of the end user, including temperature, blood oxygen level and other body parameters. Provides visual and audio feedback of target exercise parameters and/or rates to help the end user optimize his physical activity - for example a pre approved beep as a sign to slow down, a pre approved different signal/sound for signaling end user to pick up the pace and a pre defined sound for providing signal on what percentage of the exercise has been completed. Enables transfers of date to a personal computer (PC) for further analysis, review or summary. Provides visual and audio feedback, for example via pause or stop playback, if the device detects one or more of the ear buds is not capturing a heartbeat which mean a possible detach and resume playback after the device detects a heartbeat from one or both of the ear buds. Provides visual and audio feedback of target exercise parameters by changing the tempo, pitch, equalizer according to the inputted vital sign so as to raise or reduce the workout intensity of the user sub-consciously. Provides visual and audio feedback of target exercise distance by changing the temp, pitch, equalizer according to the inputted step rate and distance traveled.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) an exercise system; and    (2) a method of determining heart rate of a person during exercise.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic illustration of the earphone sensor arrangement for personal exercise device.    Light emitters (21,22,23)    Light detectors (24,25,26)    Infrared signals (30,31,32)    Waveguide channels (35,36,37)    Ear bud (50)