The main functions of Fitbit wearable devices are to track heart rate while taking steps.Therefore, Fitbit will use Heart Rate Monitoring along with tracking Walking or Running to determine calories burned and intensity of an exercise. Other activities like crossfit, swimming, biking, and others that use heart rate monitoring alone may not always appear on Fitbit. You can read a few of Fitbit community responses for crossfit here. One solution to enter exercises was to manually enter the exercise through Fitbit. You can learn how to manually enter exercises here.