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Why STAmina does not show real-time SpO₂ from Apple Watch or Garmin

Many users ask why STAmina does not display real-time oxygen saturation (SpO₂) data from devices such as Apple Watch or Garmin watches.

Short answer #

Smartwatches currently do not provide continuous real-time SpO₂ measurements during activity.

SpO₂ on these devices is measured only occasionally (spot checks or periodic background measurements), which means apps cannot receive oxygen saturation updates every few seconds during breath-hold training.

Main reasons #

There are three main reasons why real-time SpO₂ is not available in STAmina:

  1. Smartwatches do not measure SpO₂ continuously
    Most devices perform only occasional measurements rather than providing a continuous data stream.

  2. Real-time SpO₂ data is not available to third-party apps
    Even when a watch records oxygen saturation, the data is usually stored internally and not exposed as a live stream through the developer APIs.

  3. Breath-hold physiology reduces measurement reliability
    During apnea the body reduces blood flow in the extremities, which makes wrist-based optical measurements less reliable.

How SpO₂ works on smartwatches #

Most smartwatches measure oxygen saturation using optical sensors (PPG).

Unlike heart rate, SpO₂ measurements require:

  • very stable conditions
  • minimal movement
  • sufficient blood flow

Because of this, watches typically measure SpO₂ only in the following modes:

  • manual spot checks
  • occasional background sampling (for example every ~5–15 minutes)
  • during sleep

This means the watch does not produce a continuous SpO₂ data stream.

In contrast, heart rate is measured almost continuously (multiple times per second), which is why apps can show live HR but not live SpO₂.

Why does my watch show SpO₂ then? #

Some watches display SpO₂ values in their own interface.

However, this does not necessarily mean the device is measuring oxygen continuously or that this data is available to third-party apps in real time.

In many cases the watch performs only infrequent background measurements, and apps may display a graph built from those rare samples rather than a true continuous measurement.

Why this matters for apnea training #

To monitor oxygen dynamics during breath-hold training, we would ideally need SpO₂ updates roughly every 1–3 seconds.

Current smartwatches simply do not provide measurements at this frequency.

Even if an app shows an SpO₂ graph, it is usually built from infrequent background measurements, not from real-time monitoring.

Additional physiological challenges during breath-hold #

Breath-hold itself introduces physiological changes that make wrist-based SpO₂ measurements less reliable.

During apnea the body activates strong peripheral vasoconstriction, redirecting blood flow to vital organs such as the brain and heart.

As a result:

  • blood perfusion in the wrist decreases
  • optical sensors receive a weaker signal
  • SpO₂ measurements become less reliable

Cold water can further increase vasoconstriction, which is why wrist-based SpO₂ measurements during diving are particularly unreliable.

What devices can measure SpO₂ continuously #

Continuous oxygen monitoring typically requires a dedicated pulse oximeter with sensors placed on areas with strong blood perfusion, such as:

  • finger
  • ear lobe
  • forehead

These locations provide a stronger optical signal and are commonly used in medical pulse oximeters.

Using a pulse oximeter with STAmina #

If you are interested in monitoring SpO₂ during apnea training, the recommended approach is to use a compatible external pulse oximeter.

STAmina supports several sensors that can stream real-time data over Bluetooth.

See what sensors are supported.

Will this change in the future? #

Possibly.

If smartwatch manufacturers begin providing continuous SpO₂ data streams through their APIs, STAmina will be able to support them.

At the moment, however, this type of data is simply not available from current smartwatch platforms.