Cardio Fitness, available within the Gen 2 Wellness watch app, uses your resting heart rate and biometrics (e.g., age, gender, weight) to estimate your VO2max, which reflects cardiorespiratory and endurance abilities based on exercise performance. The VO2max reading is designed to convey an overall fitness level relative to your age and size. If you’re wearing your watch continuously throughout the day, you should get a reading within 24 hours. If you wear your watch for a few hours each day, it can take up to a week to get a reading.