This is it... a comprehensive list of wearable data accessible through APIs today

Fitness trackers first surfaced in 1965 with the Manpo-kei which translated to the ‘10,000 steps meter' invented by Dr Yoshiro Hatano. Dr Hatano built it at the Kyushu University of Health and Welfare whilst researching how to combat obesity and posited that 10,000 steps provide the proper balance of caloric intake and activity-based calorie expenditure to maintain a healthy body.

Since then, fitness trackers have entered mainstream markets with global spending on wearable devices exceeding 80 billion US dollars in 2021 and over 500 million units being shipped worldwide.

Wearables today track a huge range of key indicators from your heart rate to your sleep, and even your blood oxygen levels. Each indicator can be extremely useful to a user when understood properly. There is a huge range of apps today built using the data tracked on these devices. Below is a list of the data that different providers give access to through their API today:

Provider data accessible through APIs today:

Heart rate

Most wearables today use a method called photoplethysmography (PPG) to measure heart rate. PPG works by reflecting light onto skin and measuring the amount of light that is scattered by blood flow. When light enters the body, it scatters in a predictable manner as the blood flow dynamics change through changes in blood pulse rates (heart rate) or changes in blood volume. By analysing the way in which the light scatters, heart rate is calculated by the PPG sensors in your watch.

The providers that give access to detailed heart rate data through their API today are:

• Fitbit, Oura, Trainingpeaks, Withings, Cronometer, Suunto, Zwift, Garmin, Eight Sleep, Wahoo, Google, Polar, Apple, Samsung

Heart rate variability

Heart rate variability is the variation of RR intervals (length of time between ‘peaks' for each heartbeat). Some wearables using PPG to measure heart rate are also able to calculate RR intervals and deduce heart rate variability for a user by looking at the difference between each interval.

HRV data available through following APIs:

• Oura, Withings, Garmin, Eight Sleep, Polar, Apple, Samsung

Blood oxygen measurement (Pulse OX)

Pulse OX is a measurement of how saturated the blood is with oxygen and is derived from the Sp02 or peripheral oxygen saturation. It's measured using a form of PPG in which the wearables reflect infrared and red light onto the skin. The light is then reflected back to the smartwatch and the difference between the light emitted and reflected is used to determine blood oxygen level.

Pulse OX data available through following APIs:

• Oura, Withings, Garmin, Google, Apple, Samsung

Respiration rate

Respiration rate describes how often you inhale and exhale in a minute. It is derived from HRV - when you inhale the length of time between heartbeats shortens slightly and when you exhale it lengthens (respiratory sinus arrhythmia).

Respiration data available through following APIs:

• Withings, Garmin, Eight Sleep, Polar, Apple, Samsung

Sleep

Wearables measure a range of important data related to your sleep including sleep duration, sleep quality, time spent in each sleep stage (light, deep, REM, non-REM), and potential problems whilst sleeping. Older and cheaper wearable devices rely on accelerometers to auto-detect sleep whilst newer models detect your sleep from your heart rate and breathing, providing more accurate estimates.

Sleep data available through following APIs:

• Fitbit, Oura, Trainingpeaks, Withings, Cronometer, Suunto, Zwift, Garmin, Eight, Wahoo, Google, Polar, Apple, Samsung

Body temperature

Some wearables today measure body temperature using outward-facing sensors to gauge your temperature based on the external environment or based on your heart rate. Some devices use other methods. For example, the Fitbit Sense uses an Electrodermal Activity (EDA) Sensor to detect temperature changes on your body based on the variation in electrical potential between various parts of the skin. The Oura ring measures temperature every minute taken directly from the underside of your finger to give users a continuous estimate.

Body temperature data available through following APIs:

• Oura, Withings, Cronometer, Eight Sleep, Google, Apple, Samsung

GPS

Many wearables today also have built in GPS locational information.

GPS data available through following APIs:

• Fitbit, Trainingpeaks, Suunto, Peloton, Zwift, Garmin, Wahoo, Google, Apple, Samsung

Accelerometer

Accelerometers are sensors which measure the accelerations of objects in motion along reference axes. Accelerometry data can be used to derive velocity and displacement information. In wearables, accelerometers are often used with a number of other sensors to determine many factors including step count, calories burned, etc.

Accelerometer data available through following APIs:

• Fitbit, Withings, Garmin, Wahoo, Google, Polar, Apple, Samsung

Glucose

A continuous glucose monitor is a small device that you wear under your skin that measures your glucose (sugar) levels continuously throughout the day and night, letting you see trends in your levels and alerts you to highs and lows.

Through the Terra API, we provide connections to all of these wearables and their APIs.

As always, please let me know if I'm missing any important data fields!