Embodiments provide physiological measurement systems, devices and methods for continuous health and fitness monitoring. A wearable strap may detect reflected light from a user's skin, where data corresponding to the reflected light is used to automatically and continually determine a sequence of instantaneous heart rate of the user. Specifically, the heart rate of the user may be determined through the use of a peak detection algorithm that determines an R-wave-to-R-wave interval (RR interval). Based on the confidence of the RR interval, the peak detection algorithm or a frequency analysis algorithm may process the reflected light data to determine the sequence of instantaneous heart rates of the user.
