From Marco Altini:
The only scientifically validated HRV app that doesn't require an external sensor. HRV4Training helps you optimize your goals and prevent overtraining by measuring your Heart Rate Variability and providing tailored feedback on your physical condition. HRV4Training does not require a heart rate monitor, since it can accurately assess your HRV using the phone's camera. HRV4Training is also the first app that goes beyond simple measurements and provides insights on: 1) acute or day to day HRV changes in response to different stressors (alcohol, travel, sick days, training, menstruation, etc). 2) long term multi-parameter trends to look at the big picture. 3) correlations between physiological measurements and annotations. 4) training load analysis, fitness, fatigue, readiness to perform and injury risk. 5) VO2max estimation for runners linking the app to Strava or TrainingPeaks. 6) Training Polarization analysis (or 80/20). 7) Weekly and monthly summaries to track progress. All data is processed inside the app in order to provide you with actionable interpretations that can help optimizing your training plan and performance. Supported devices for the camera measurement: iPhones 5, 5S, 6, 6S, 6+, 6S+, SE, 7, 7+. Currently unsupported devices for the camera measurement: iPhones 4S, iPads and iPods - These devices require a chest strap. Other features: HRV-based advice helps you to adapt your trainings based on objective measures of recovery. TAGS: lets you tag your sleep, mental energy, muscle fatigue, stress and all other parameters that can help you understand what is influencing your physical condition and physiological stress. Works with Bluetooth SMART heart rate monitors (a Polar H7 is recommended) or simply your phone's Camera. Configurable test (single or orthostatic, choose test duration between 1, 3 or 5 minutes). Extracts and stores the following features while lying down and/or standing: heart rate, mean of beat-to-beat intervals (AVNN), standard deviation of beat-to-beat intervals (SDNN), square root of the mean squared difference of successive R-Rs (rMssD), number of pairs of successive R-Rs that differ by more than 50 ms (pNN50), low frequency power (LF, 0.04-0.15 Hz), high frequency power (HF, 0.15-0.40 Hz). Shows the PPG signal view to ensure signal quality during the test if the camera is used instead of a bluetooth SMART sensor. HRV4T Recovery Points to provide a single, straightforward metric to analyze your physical condition. Population summaries and people like you comparisons to put your data into perspective. Analysis of compliance and consistency. Integrates with the Health app (writes heart rate, and sleep, read sleep time). Data export via email or Dropbox. Integrates with TrainingPeaks, SportTracks, Genetrainer and Strava. More details on HRV and app usage are available here: http://www.hrv4training.com/quickstart-guide.html. More details on HRV using the phone's camera are available here: http://www.hrv4training.com/blog/heart-rate-variability-using-the-phones-camera. HRV4Training requires to register an account with your email address, so that your data can be backed up safely and retrieved in case anything happens (app issue, changing phone, etc).