Overtraining can lead to exercise addiction which can lead to negative physiological and psychological effects, constant muscle soreness, elevated resting heart rate, burnout, reduced variability, elevated blood pressure, lack of appetite, and even becoming moody. To get the best out of the app you need a heart rate sensor that conforms to the Bluetooth 4 Heart Rate Service (HRS) like the Polar H7 Smart, Wahoo TICKR, Bose Soudsport Pulse, etc. You don’t have a heart sensor: The following functions are available if you don’t have a bluetooth heart sensor or Apple Watch: - Calculate your VO2 Max doing a 1½ mile run. - Calculate your Maximum heart rate. - Get optimal heart zones depending on your fitness goals (fat burn, cardio, et.c). - References and reading material on how heart rate zones are used in fitness & sports sciences. Data Privacy: - Your data remain private in your iOS Device or iCloud Account. You are in control over who views or uses your data. - This app works seamlessly with Apple Health - You do not need any annoying login accounts. - All data is stored on your iPhone/iPad/Apple Watch, and no data is on any external database on the internet or worldwide web. Battery: - Continued use of GPS running in the background can dramatically decrease battery life. - Continued use of the Apple Watch heart rate sensor can dramatically decrease battery life. - Viewing your heart rate in Graph mode will impact your battery life when the App is automatically (the icon with the wheel at the top) adjusting the XY-Axis. Tap on the wheel/settings icon at the top to switch to manual mode to conserve battery life and reduce the graphics power processing requirements. Thank you for your time, and for support or new features request, send me an email from within the App: About | Contact or tweet @ZoneTrainingApp