Questions about the Cardiio-Heart Rate Monitor + 7 Minute Workout app ("Cardiio")

Q1. Is Cardiio a medical device?

No, Cardiio is not for medical use. If knowing your pulse rate is critical to your health, you need to have your pulse taken by a medical professional. Cardiio is not intended to diagnose, prevent or treat any condition, or to be a substitute for professional medical care. Measurements and statistics are intended for informational and educational purposes only, to support general health and wellness. The Cardiio app has not been tested with individuals with health conditions, is not a clinical pulse oximeter and has not been cleared or approved by the U.S. Food and Drug Administration.

Q2. How does Cardiio measure heart rate?

Blood absorbs light. Every time your heart beats, the blood flow to your face and finger increases, causing more light to be absorbed. In between beats, less light is absorbed. By using your smartphone camera to capture tiny changes in reflected light from either your finger or face, Cardiio can calculate your pulse rate (heart rate). Cardiio is based on technology licensed from MIT and originally developed at the MIT Media Lab. MIT has not endorsed the Cardiio app or Cardiio, Inc.

Cardiio, Inc. has published several studies in peer-reviewed scientific journals validating the accuracy of the Cardiio app in measuring heart rate at rest, and after exercise (Yan et al., JMIR mHealth and uHealth, 5.3, 2017; Poh & Poh, Telemedicine and e-Health, 2017).

Important: Cardiio is intended to provide you with information that relates to maintaining or encouraging a general state of health or a healthy activity. The heart rate readings are for reference only, and Cardiio is not responsible for the consequences of any erroneous readings. Heart rate measurements should only be taken when you are still and not during an activity such as exercise. Please understand that there are inherent limitations with Cardiio’s heart rate measurement technology that may cause some of the heart rate readings to be inaccurate under certain circumstances. These circumstances include the user’s physical characteristics, the user’s health conditions, the positioning of the user’s finger or face, movement of the user or device, tremors, temperature, altitude, ambient lighting, and the type and intensity of the activity.

Q3. How do I use the finger mode to measure heart rate?

Finger placement and the amount of finger pressure are very important for proper measurement. The finger mode is also sensitive to movement artifacts. Sometimes this takes a little trial and error to learn the correct technique. Please follow these instructions:

  • Make sure your fingers are not cold.
  • If you use a case for your iPhone, please remove it as the case may interfere with a measurement.
  • Make sure that your index finger covers the entire back camera.
  • If the signal strength is too low, try covering both the back camera and the flash light with your index finger. You'll need to use two hands: one to hold the iPhone, and the other to cover the camera and flash.
  • Do not press your finger against the camera too hard (this restricts blood flow to your finger).
  • Keep both your finger and the iPhone steady throughout the measurement process. Do not move.

Q4. How do I use the face mode to measure heart rate?

The face mode is sensitive to movement artifacts and ambient lighting. Please follow these important instructions:

  • Make sure your face is well and evenly illuminated (a well-lit area is necessary).
  • Make sure your face is clearly visible (e.g. no long hair covering your forehead etc.), and that you are not sweating perfusely.
  • Do not have a bright background behind you (backlight) - it makes your face appear dark in contrast.
  • Look straight ahead (instead of looking down) and hold your iPhone/iPad with two hands, around 6 inches from your face.
  • Make sure your face fills the entire red circle.
  • Keep both your body and the iPhone/iPad still throughout the measurement process. Do not talk.
  • Breath slowly. Heavy breathing can cause movement artifacts that may affect measurement accuracy.

Q5. What is the difference between the "Rest" and "Active" tags?

At the moment, Cardiio only allows two tags for heart rate measurements:

  • Rest: You can tag measurements taken when your body is rested as “Rest”. Strictly speaking, your true resting heart rate is the number of times your heart beats per minute while your body is completely at rest, which is usually upon awakening.
  • Active: You can tag measurements taken when your body is still after physical activity as “Active”. Note that Cardiio cannot measure your heart rate during exercise as it requires you to keep still.

Q6. What does the waveform/graph represent?

The waveform/graph illustrates the quality of the pulsatile signal being detected to help you know if you are using the app properly. If the quality of the signal is poor, the heart rate readings may be inaccurate. The waveform is provided for reference only. It is not an electrocardiogram (ECG), is not intended to be utilized for medical purposes and is not intended to be used to diagnose, cure, mitigate, treat, or prevent any disease.

Q7. How does Cardiio calculate my fitness level?

Normal heart rate varies from person to person. Cardiio's fitness level rating is drawn from a generalization of typical resting heart rate levels and physical conditions (source). Naturally, there are many factors other than fitness levels that may account for changes in heart rate, including air temperature, body position, body size, and medication use (learn more). The fitness level presented is intended to be an estimation of your metrics, but may not be completely accurate.

Q8. How does Cardiio estimate potential life expectancy?

Cardiio estimates potential life expectancy based on your average resting heart rate as measured by the app, and gender and age as entered by you. Our estimation considers the hypothesis that resting heart rate is inversely related to life expectancy (Levine, Journal of the American College of Cardiology, 30.4, 1997; Zhang & Zhang, Ageing Research Reviews, 8, 2009), and uses the life expectancy data from a National Vital Statistics Report published by the U.S. Department of Health and Human Services (HHS) and Centers for Disease Control and Prevention (CDC). This is a hypothetical calculation that is purely an estimate and not intended to measure accurately life expectancy.

Q9. How does Cardiio calculate my endurance score?

Cardiio calculates an endurance score based on the ratio of your estimated maximum heart rate using the gender, age, and weight you entered, and your average resting heart rate as measured by the app (Uth et al., European Journal of Applied Physiology, 91.1, 2004). This is a hypothetical calculation that is purely an estimate of your endurance.

Q10. How does Cardiio provide the "How You Stack Up" comparisons?

Our data for the average heart rates for a US adult male and female are from a National Health Statistic Report published by the U.S. Department of Health and Human Services (HHS) and Centers for Disease Control and Prevention (CDC). Heart rate data about celebrities are based on online reports or news articles, not intended to be current or accurate, and are for entertainment purposes only.

Q11. How does Cardiio provide age/gender specific comparisons?

Our data for age- and gender-specific resting heart rate percentiles are from a National Health Statistic Report published by the U.S. Department of Health and Human Services (HHS) and Centers for Disease Control and Prevention (CDC).

Q12. How does Cardiio calculate my target heart rate?

Cardiio estimates your target heart rate (HR) using the Karvonen method, which takes your average resting heart rate into account. The formula is as follows:
target HR = (max HR − resting HR) × %Intensity + resting HR

For example, John is 40 years old and his average resting heart rate is 58 bpm. What is his target heart rate for the 60-70% intensity exercise zone?
Max HR = 220 - age = 220 - 40 = 180
Lower limit = (180 - 58) × 0.6 + 58 = 131
Upper limit = (180 - 58) × 0.7 + 58 = 143

John's target heart rate in the 60-70% intensity zone is 131-143 bpm.

The target heart rate calculator provides general reference information and is not intended as a substitute for consulting with your physician. Please make sure to consult with your physician before you start to exercise.

Q13. How does Cardiio estimate my caloric burn?

During moderate to vigorous activity, there is a linear relationship between heart rate and oxygen consumption. This heart rate-oxygen consumption relationship is subject to both intra- and inter-individual variability. To estimate your energy expenditure, we use a mixed-model analysis that accounts for your gender, heart rate, weight, estimated endurance score, duration of activity, and age (Keytel et al., Journal of Sport Sciences, 23.3, 2005). This is purely an estimate and not intended to measure accurately caloric burn.

Q14. How do I use the calorie-burn estimator?

To use the calorie-burn estimator, you need to measure your heart rate after you've exercised, tag it as an "Active" heart rate (choose "Active" in the Save prompt when your heart rate measurement is complete), and enter an exercise duration (in minutes). In addition, you'll need to have a recent "Rest" heart rate measurement for a baseline. Note that this is purely an estimate and not intended to measure accurately caloric burn.

Please check to make sure your settings are right:

  1. Go to “History” to access your saved data.
  2. Tap into a specific day to see the individual saved measurements.
  3. Make sure that they are correctly labeled as "Rest" or "Active" (you can change the label by swiping).
  4. For "Active" measurements, make sure that you've entered the exercise duration. Tap on the number to change it.
  5. Once completed, return to the "Insight" screen. If you have "Active" measurements recorded today, your calories should be displayed. NOTE: If the measurements were in the past 7 or 30 days, you need to swipe the top gray panel ("TODAY") to the left to view them.

Other things to consider:

  1. If the message "calories unavailable" appears, it means that you need to measure your resting heart rate and save it.
  2. If the message "active heart rate too low" appears, it means that the amount of physical exertion was not high enough to estimate caloric burn

Q15. How do I restore my PRO purchase on my iPad/iPhone?

Go to Cardiio > Settings > Restore purchases, then tap on it. You'll be prompted to enter your Apple ID and password. Once Apple has verified your previous purchase, the features should be unlocked.

Q16. How do I sync Cardiio with Apple Health?

Please note that the measurements from Cardiio are for educational, research, fitness and general wellness purposes only. Measurements from Cardiio are not intended to be used for any medical purposes. To connect with Apple Health:

  1. Go to Cardiio > Settings > Apple Health. Tap on it and swipe the slider next to heart rate to green to grant the app permission to sync, then tap 'Done'.
  2. Save a new heart rate measurement using the Cardiio app (Make sure you wait around 20 seconds for the Save prompt to appear).
  3. Check for your data:
  4. Launch Apple Health > Tap on 'Health Data' > 'Vitals' > 'Heart Rate' > 'Show All Data'

Q17. How do I pair Cardiio with RunKeeper?

  1. Go to Cardiio > Settings > Options and you'll see the button for RunKeeper (it should say "Not configured" unless you're already connected).
  2. Tap on the RunKeeper button and enter your account details to login. Note: Don't login via Facebook! In the current release there is an issue with the RunKeeper Facebook login. As a workaround, simply use the email address registered with your Facebook account, along with your RunKeeper password to login instead.
  3. Grant Cardiio permission to be paired with your RunKeeper account. The RunKeeper button should now say "Authorized".
  4. You're all set. Now your heart rate measurements will be automatically posted to your RunKeeper feed!

Q18. How do I receive the latest news and updates from Cardiio?

To stay up-to-date, follow us on Twitter @cardiio or Like us on Facebook!

Other questions?