The technology

The iD.RUN uses photoplethysmography (PPG) technology to record heart rate from the surface of the skin (wrist). This method eliminates the need for a chest strap.

How does PPG work?

The PPG shines light on the skin. An optical sensor measures the reflection of the light. The heart rate is determined by measuring how much blood passes through the illuminated spot as the heart beats.


Guidelines to consider

For the most accurate heart rate measurement, the watch should be worn snugly on the middle of the wrist. The watch should sit flat on the skin and ambient light should be avoided under the device.

Therefore, the watch should be worn at least 2 cm away from the wrist (towards the arm).

The watch should sit snugly against the skin without cutting off circulation and restricting blood flow. The wrist band can be finely adjusted to fit nearly any size.

How precise is the measurement?

The rule of thumb regarding the accuracy of the measurement method is: PPG may vary by +/- 5 beats compared to the chest strap.

Given the accuracy and length of time to measure heart rate with PPG, it may not be suitable to control interval training.

In constant conditions (constant pace, constant gradient, not too high intensity), the measurement is comparable to the chest strap.

Other factors for accurate measurement

There are a multitude of factors that affect the measuring accuracy of PPG.

Blood circulation

Blood circulation varies from person to person and may also differ intra-individually (for example, between the left and right arms). In some cases, natural blood flow may not be optimal for PPG measurement in certain individuals.

Environmental factors

If the ambient temperature is too low, blood flow to the forearms will be affected and PPG measurement accuracy may decrease.


Improper posture (such as sharply bent wrists) will affect the circulation of the forearms and reduce PPG measurement accuracy.

The colour of the skin surface also influences the reflectivity. In principle, the less light is absorbed through the skin surface, the better the PPG measurement. Strong pigmentation of the skin, scarring and tattooing can therefore adversely affect the measurement accuracy.

PPG vs. ECG (chest strap)

Photosensor Electrodes
Reflection changes due to blood flow under the skin Electric signal of the heart
Longer measurement time: Motion artefacts and ambient light need to be corrected. Immediate availability of the heart rate

Which technology is right for me?

Yes No
Do you frequently perform interval training and control this via the heart rate?
Do you want to wear your watch outside of clothes in winter?
Do you want to measure the heart rate while swimming?
Does a chest strap interfere during sports?
Do you want to measure your heart rate every now and then during the day?
Accuracy Comfort
What is more important to you in sports?



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