Why is my fitness session shorter than the duration I exercised for?

There are a few factors that could influence a discrepancy between the duration of an actual fitness event and what the data shows in the app. 

Firstly, the PPG sensor in your wearable that captures your heart rate is influenced by how well your wearable fits. It is important to wear your wearable device properly to ensure it can measure heart rate under optimal conditions. Both wearing the wearable too tightly or too loosely can negatively affect the quality of the PPG signal. 

We recommend the following to improve PPG signal during exercise.

1. Place the wearable further up your wrist in order to prevent motion artifacts. This is especially important if you will be doing exercise that involves a lot of wrist and arm movement (for example, walking, cycling, weight-lifting, and rowing).
2. Warm up before you start your exercise session. This will increase blood flow to the extremities and improve blood flow. 
3. If it is cold, wear warm clothing to avoid poor blood flow. Take care to place tight-fitting sleeve cuffs away from the device so that they do not put pressure on it.
4. Once the wearable has started monitoring your heart rate, wait for a few seconds or until the wearable reports a valid heart rate, before you start exercising. That way, you can be sure that the wearable is accurately measuring your heart rate.

Secondly, the recording of fitness events is heavily influenced by heart rate. The wearable picks up an exercise event automatically based on heart rate elevation and movement. This means that if there are any breaks in an exercise event, such as in some forms of stationary strength training or stationary cycling, the accuracy of the start and stop times of a fitness event will be influenced. The heart rate and movement segments within a fitness session must be at least 10 minutes long to be added to the session. Any moderate or vigorous heart rate elevations, whether it was included in the fitness session or not, will still contribute to your overall score.