Systems and methods for identifying and presenting information regarding a fitness cycle using earphones with biometric sensors are provided. Fatigue level associated with fatigue experienced in response to a stimulus and recovery from such fatigue may be determined based on heart rate variability (HRV) data and learned user characteristics. One or more cycles of fatigue and recovery can be identified as a fitness cycle(s), each fitness cycle encompassing a period of time beginning with the stimulus associated with the fitness-related activity and progressing through recovery from the fatigue experienced in response to the stimulus associated with the fitness-related activity. Information regarding the fitness cycle(s) can be presented to a user in a variety of ways, including on a display of a computing device in communication with the earphones with biometric sensors.
