fēnix 3 is packed with training features to tell you about your form and fitness. The first is the VO2 max estimator. When used with a heart rate monitor¹, fēnix 3 crunches data, including your running speed, beats per minute and heart rate variability to estimate the maximum volume of oxygen you can consume per minute. Track changes to your VO2 max to see your fitness gains and to compare with your peers. Other fitness metrics include recovery advisor with a recovery timer and recovery check, plus a Race Predictor, which estimates your ideal finish time based on your current VO2 max number.