Fitness trackers use a variety of methods to measure heart rate, but the most common is photoplethysmography (PPG).
Photoplethysmography (PPG)
PPG works by shining a light, usually green or red, onto your skin. The light passes through your blood vessels and is reflected back to the tracker. The amount of light reflected back changes depending on the amount of blood flowing through the vessels. Since your heart pumps more blood when it beats faster, the tracker can detect these changes in light reflection and calculate your heart rate.
Different Types of PPG Sensors
There are several types of PPG sensors used in fitness trackers:
- Green LED sensors: These are the most common and typically found in wrist-worn trackers.
- Red LED sensors: These are less common but can be more accurate in some cases.
- Infrared LED sensors: These are used in some trackers to measure blood oxygen levels.
Factors Affecting Accuracy
The accuracy of PPG heart rate measurements can be affected by several factors:
- Movement: Shaking your wrist or moving your arm can interfere with the sensor's ability to measure heart rate accurately.
- Skin Tone: People with darker skin tones may have more difficulty getting accurate readings.
- Placement: The placement of the sensor on your wrist can also affect accuracy.
- Temperature: Extreme temperatures can affect the accuracy of PPG readings.
Alternatives to PPG
While PPG is the most common method, some fitness trackers use other technologies to measure heart rate, such as:
- Electrocardiogram (ECG): This method uses electrodes to measure electrical activity in the heart, providing more accurate measurements but requiring a more complex device.
Conclusion
Fitness trackers use PPG technology to measure heart rate by detecting changes in blood flow through the skin. The accuracy of these measurements can be affected by movement, skin tone, placement, and temperature. While PPG is the most common method, some trackers use other technologies like ECG for more accurate readings.
