Garmin Pulse Ox

Plain English: The watch shines red and infrared light into the wrist to estimate how much of the blood’s oxygen-carrying capacity is in use. Garmin says a reading should generally be 95% or higher, and that numbers below 90% may be considered low. A lower reading at altitude is normal and tends to rise as the body acclimatises.

In practice: I’ve found notable and regular deviations of up to 4 percentage points from finger sensors. 

Quick answers

What is a normal Pulse Ox reading on Garmin?
Garmin says the value should generally be 95% or higher in most settings, and that numbers below 90% may be considered low, citing the Mayo Clinic. At altitude the normal range is lower, and readings in the low 90s are common in the first days above about 2,500 m.

Is Garmin Pulse Ox accurate?
It is accurate enough for trends but not for medical decisions. A 2023 study of 49 adults found a mean absolute error of 5.8% on a Venu 2S with 14% of readings missing, and Garmin states the feature is not for medical use.

Why does my Garmin Pulse Ox show very low numbers at night?
Sleeping position is the usual cause. A wrist that is compressed or tucked under the body restricts blood flow to the sensor, and Garmin notes that unusual positions can produce abnormally low readings. Readings that stay low across several nights in different positions are worth checking with a finger oximeter.

Does Garmin Pulse Ox drain the battery?
All Day mode does, because the optical sensor wakes repeatedly to take readings, and Garmin acknowledges a significant battery penalty without quantifying it. During Sleep mode gives an overnight trend at far lower cost.

Pulse Ox – a deep dive

When Pulse Ox is actually useful

This is useful as a silent input to Garmin’s breathing disruption and altitude acclimation metrics, so let it do its job. Pulse Ox (SpO2) is a medical vital sign, but you should only use Garmin’s estimate as a prompt to check with an accurate medical-grade device if your health is poor. It does read low for me after a hard workout or when I’m ill, as I would expect. However, it now generally seems to run lower than it did several years ago, when Garmin first released Pulse Ox. It read higher for me then, and more in line with what I would expect day to day.

Introduction

Garmin Pulse Ox estimates the percentage of oxygen saturation in the blood (SpO2) from red and infrared light shone into the skin by the optical sensor on the back of the watch. Garmin says the value “generally speaking” should be 95% or higher, and that numbers below 90% may be considered low. The feature arrived in 2018, with Fenix 5X Plus among the first watches to carry it.

Pulse Ox is most useful at altitude, where saturation falls and a rising trend marks acclimatisation. Its limitation is accuracy, because validation studies find a wrist estimate noticeably weaker than a medical finger oximeter, and Garmin states the feature is not for medical use.

What Pulse Ox actually means

The figure is an estimate of peripheral oxygen saturation, the proportion of haemoglobin carrying oxygen. At sea level a healthy adult normally sits between 95% and 100%, and readings of 90% to 94% that persist deserve attention. Garmin quotes the Mayo Clinic for the 90% line. Normal saturation barely varies with age, sex or fitness, so a trained athlete does not read higher than anyone else. The range is narrow, which is why a few points of wrist error matter. At altitude the partial pressure of oxygen falls, and readings in the low 90s or upper 80s are common in the first days above about 2,500 m.

How Garmin calculates Pulse Ox

Garmin states that the sensor uses red and infrared light. Oxygenated and deoxygenated haemoglobin absorb the two wavelengths differently, so the ratio of absorption gives an estimate of saturation, which is the principle used by finger oximeters. Garmin does not publish the calibration or signal processing, and does not attribute the figure to its Garmin Human Performance Lab engine.

Modes vary by watch. An on-demand spot check needs the wearer to stay still with the wrist at heart level and is cancelled if motion is detected. During Sleep records the sleep window, and All Day takes periodic readings whenever the wearer is stationary. With sleep tracking on, compatible watches also report breathing variations as minimal, a few, occasional or frequent, which Garmin presents as a wellness indicator rather than a diagnosis. The Altitude Acclimation widget combines Pulse Ox with respiration rate and resting heart rate above 800 m and needs All Day mode.

What affects the reading

Motion is the largest factor, and even fidgeting during a spot check can prevent a reading. Fit matters: Garmin advises a snug strap above the wrist bone and a clean, dry sensor, because lotion, sunscreen and repellent can interfere with the light signal. Cold constricts blood vessels in the extremities and can stop the sensor finding a signal.

Skin pigmentation affects all optical oximeters. Jiang and colleagues found no statistically significant difference in error across Fitzpatrick skin tones for the Garmin watches they tested, although the sample was small. Sleeping on or under the wrist restricts blood flow and can drag a night’s readings far below the truth, which is why a single low overnight value tells an athlete little.

How accurate is Garmin Pulse Ox

Absolute accuracy is moderate to poor. Jiang and colleagues (2023) tested 49 adults with respiratory conditions against a Masimo reference. The Venu 2S had a mean absolute error of 5.8% with 14% of readings missing, and the Fenix 6 Pro lost 28% of readings. An Apple Watch Series 7 in the same study had 2.2% error. Coll and colleagues (2021) tested a Forerunner 245 in 10 healthy subjects at simulated altitudes of 3,000 to 5,500 m. The watch tended to overestimate, more than half of readings fell outside a 3 percentage point tolerance, and the share rose above 80% at the highest altitudes. The authors advised against using it for acclimatisation decisions.

Weinrauch (2023) found that 53 of 100 attempts on a Fenix 6 Pro at sea level failed, 38 falling outside 3 points of the reference and 15 returning no reading. These studies used older sensors, and no independent validation of newer hardware has been published. Trend reliability over several nights has not been formally studied for any Garmin watch.

Competitor equivalents

• Apple Watch has a Blood Oxygen feature on the same optical principle, and its availability in the United States has changed with the Masimo patent dispute.
• Polar offers SpO2 on a limited number of models, including Vantage V3 and Grit X2 Pro, and most Polar watches have none.
• Coros includes SpO2 on many watches, with on-demand, sleep and altitude acclimation modes.
• Suunto offers SpO2 on Race 2 and some other models, with manual and sleep modes.
• Stryd is a foot pod and has no SpO2 measurement.

Coros, Suunto and Apple all describe their implementations as non-medical, as Garmin does.

Which Garmin devices support Pulse Ox

Pulse Ox needs Garmin’s red and infrared optical sensor, which Garmin introduced in 2018 and now includes across the Forerunner, Fenix, Epix, Venu, Vivoactive and Instinct ranges and others. The modes vary by watch and firmware, with older models offering only on-demand and sleep readings, and the feature is not available in every country. Garmin’s page for each model lists what it supports.

Where to find Pulse Ox on Garmin

• Watch glance: viewing it while still starts a spot check, and it shows the latest percentage, a 24-hour hourly average, a 24-hour elevation graph and a seven-day trend.
• Garmin Connect mobile, Health Stats: the latest reading, the overnight trend when sleep mode is on and longer-term trends.
• Garmin Connect web, Health: a less detailed view than the app.
• Altitude Acclimation widget: weekly Pulse Ox averages alongside respiration rate and resting heart rate, where the watch offers it.

Common problems and misreadings

Missing readings are the commonest complaint, and the tests above recorded 14% to 28% missing on Garmin watches. Wearers who sleep with the wrist tucked under a pillow or body see the largest gaps.

Alarming overnight lows are usually positional. A compressed wrist can push a short stretch of the night into the low 80s or 70s, and the false-positive rate is why Garmin sends no low-SpO2 alert. See Quick answers above.

A watch that disagrees with a finger oximeter is behaving as expected. The fingertip has strong, consistent pulsation and the wrist does not, and differences of 3 to 5 points sit within the documented error range of the technology.

How to improve Pulse Ox

Blood oxygen saturation is not a trainable metric, because a healthy athlete at sea level already sits near the ceiling regardless of fitness; at altitude, gradual ascent and time bring the reading up as the body acclimatises.

Scientific basis

Jiang and colleagues. PLOS Digital Health, 2023, 2(7): e0000296. Compared Garmin and Apple wrist SpO2 with a Masimo reference in 49 adults and is the source of the Venu 2S and Fenix 6 Pro figures above.

Coll, Richalet and Lhuissier. International Journal of Sports Medicine, 2021, 42(14): 1268-1273. Showed the Forerunner 245 overestimating SpO2 at simulated altitude, which is the condition where acclimatisation decisions would rely on it.

How Pulse Ox connects to other Garmin features

Pulse Ox feeds the Altitude Acclimation widget alongside respiration rate, and the overnight breathing-variations insight uses the same sleep window as Sleep Stages. A saturation dip with a rise in breathing rate is the pattern the acclimation widget tracks, and it can coincide with a fall in HRV Status when the body is under illness or altitude stress.