Learn how to read your SpO2, this is how your GPS sports watch helps you to train better

Just one fact, but a relevant one. In 2024, 73% of runners will use GPS devices for training, according to the Global Running Survey. This makes it clear that the use of wearables and heart rate monitors & sports watches with GPS has grown significantly in recent years. To a large extent, this percentage responds to the search for more accurate information on the performance and physical condition of each person, as well as the possibility of sharing achievements and routines on platforms such as Strava, Komoot, Garmin Connect and Runalyze, among others.

GPS running watch: The best running watches of 2025

Among all the metrics that we can nowadays consult on a GPS sports watch -such as pace, distance, heart rate or calories burned-, another increasingly valued measurement has been gaining ground: blood oxygen saturation (SpO2). This figure indicates the percentage of hemoglobin in the blood that is carrying oxygen at any given time.

Why is the SpO2 function relevant for a runner?

Basically because oxygen is the gasoline that fuels our muscles and, to a large extent, determines the level of performance we can achieve. When our oxygen saturation is maintained at optimal levels, we feel more agile and less fatigued, while a drastic decrease can translate into excessive fatigue or even risk of overtraining.

In RUNNEA we explain you, in a direct and simple way, what are the benefits of measuring your SpO2 with the help of GPS heart rate monitors & sports watches and how we can take advantage of it to improve our performance as a runner.

What are the benefits of SpO2 for runners?

As a general rule we associate SpO2 measurement with clinical settings or high altitude contexts, but the reality is that every day more and more popular runners are taking advantage of this data to make a leap in quality in our training, at the same time that we take care of our health.

Thus, the three major advantages of measuring blood oxygen saturation are:

• Optimization of training.
• Prevention of overtraining.
• Adaptation to altitude.

Let's take it one step at a time...

Training optimization

One of the keys we have to improve our running skills is to train intelligently and know when it is convenient to work on aerobic and when to move to more demanding or anaerobic rhythms. SpO2 can give us clues about our body's oxygenation capacity at different exercise intensities.

Aerobic/anaerobic threshold detected by SpO2 variations

When we run below the anaerobic threshold, our body is able to supply enough oxygen to the muscles, so fatigue takes longer to appear. If the oxygen saturation remains stable at around 95-99%, we can assume that we are training in the aerobic zone.

Conversely, if SpO2 begins to drop sharply, we are probably forcing the body into the anaerobic zone.

Case study: adjusting paces using marathon oxygenation data

You are preparing for the marathon and, of course, your GPS watch with SpO2 sensor is a must on your long runs. If we notice that, at a certain pace, your saturation drops to values close to 90% and we feel too fatigued, it will be an indicator thatwe should adjust the speed. In this way, you avoid "burning out" before your time and ensure that you maintain a sustainable effort throughout the race.

Preventing overtraining

Over-training is a common problem among popular runners, often resulting in injury, performance drops or parking. Measuring SpO2 can be a simple way to anticipate when our body is at its limit.

Relationship between SpO2 drops and accumulated fatigue

When we accumulate fatigue, our cardiovascular and respiratory systems can be affected. In the morning, we may register a lower than usual SpO2 level, indicating that the body has not fully recovered. In that sense, if we detect a pronounced drop in the days following demanding workouts, it is a sign that the body needs rest or a lighter training volume.

Comparative table: optimal vs. alert levels

• Between 95%-99%: Optimal level. Indicates good recovery and balanced training.
• Between 90%-94%: Moderate level. May indicate incipient fatigue or accumulated fatigue.
• Below 90%: Alert level. It usually reveals possible overload, lack of recovery or problems adapting to the intensity of training.

Adaptation to altitude

Many runners have made training at altitude a strategy to improve oxygenation and gain extra endurance. However, it is essential to keep a strict control of hypoxia, or in other words, lack of oxygen.

Hypoxia monitoring during high-altitude workouts

When ascending above 15002,000 meters, it is common for oxygen saturation to drop naturally. Thanks to the continuous measurement of SpO2 on our GPS watch, we can observe in which range we are moving and detect if the drops are excessive, something that could lead to dizziness, headaches or, in extreme cases, high altitude pulmonary edema.

SpO2 technology in GPS heart rate monitors & sports watches

In order to measure SpO2 reliably, the latest generation of GPS heart rate monitors & sports watches have been incorporating optical pulse sensors similar to those used in medical oximetry. However, not all sensors perform equally well or offer the same accuracy.

Analysis of optical vs. traditional sensors

Optical sensors use LED lights that are able to pass through the skin to measure the amount of oxygen in the blood. Their advantages lie in the possibility of continuous measurement and the absence of wires. On the other hand, more traditional methods (such as chest straps or finger pulse oximeters) can be more accurate, although less practical for training.

Interpretation: A margin of error of 2 or 3 means that readings may vary slightly from actual saturation. Still, using these values as a trend, they are sufficient to detect significant changes in oxygenation during training and rest periods.

What features should GPS heart rate monitors & sports watches have to measure blood oxygen?

Not all heart rate monitors & sports watches offer the same quality of SpO2 measurement. For your data to be reliable and effective, it is essential to look at certain aspects:

• High-quality optical sensor: it is obvious, but we should go for devices that have a specific optical sensor for SpO2, not only for heart rate. LED illumination technology and calibration are essential for consistent readings.
• Customizable sampling frequency: some watches allow you to adjust how often the measurement is taken (every 15 seconds, 30 seconds, or 1 minute). The more frequent the sampling, the more detailed the oxygenation grwill be, but also the higher the battery consumption.
• Accuracy checked in independent tests: before deciding on a model, it is advisable to consult reviews and comparisons that analyze its margin of error.
• Connectivity and analysis software: beyond the measurement, you will need a platform or app that shows you clear trends, allows you to compare with your pace, heart rate or altitude, etc. Brands such as Garmin, Huawei, Polar, Apple or Coros, among others, usually offer quite complete environments for the runner.
• Battery life: SpO2 measurement can drain the battery quickly, especially if used continuously. Make sure your watch has a power-saving mode or the ability to withstand your longest workouts without running out of charge.

How can you integrate blood oxygen measurement into your workouts?

In addition to knowing the theoretical benefits of SpO2, it is essential to know how to put these measurements into practice on a regular basis, so that the data becomes a real tool for improvement.

• Planning the week: at the beginning of each training cycle (e.g. every Monday), we review the SpO2 averages of the previous week to decide whether to increase the load (if the values have been good) or lower the intensity (if you have seen significant decreases).
• Fatigue monitoring: we supplement oxygen readings with resting heart rate and sleep quality. If we notice that your SpO2 drops below the usual range and our resting heart rate rises, we may need active rest days or lighter sessions.
• Use in interval training: for those who practice intense series, it is convenient to check the SpO2 at the end of each interval or in the recovery between repetitions. If we observe that we do not recover an acceptable level of oxygenation, we may need to extend our rest period.
• Progressive adaptation: if you have the opportunity to train at altitude, increase the altitude gradually while controlling your oxygenation. Make decisions to climb or stay at that altitude level depending on how your SpO2 responds, avoiding abrupt jumps that may entail risks.

In the practicalguto the use of SpO2 we highlight:

Protocol for reliable measurements.

• Correct position of the watch: the device must fit snugly on the wrist, without being too loose or too tight.
• Environmental conditions: extreme cold or high humidity may affect peripheral circulation and, consequently, the accuracy of the measurement.
• Frequency of reading: it is necessary to determine whether you want to measure SpO2 only at certain times (e.g. upon waking and before going to bed) or continuously during exercise.

Interpretation of nocturnal vs. activity trend gr

• Overnight trend: some watches allow SpO2 to be monitored while we sleep. If our levels remain stable (95%-99%), it indicates that our body has recovered adequately. Constant drops below 90% may suggest recovery problems or sleep disorders.
• In activity: during running or more intense workouts, saturation may drop slightly. It is useful to observe how long it takes to return to normal values after the completion of an interval or a series of sprints, as this reflects our body's ability to recover.

Measuring blood oxygen saturation, a relevant metric, but not the only one

With all that we have told you, the measurement of blood oxygen saturation (SpO2) represents a very powerful tool for all types of runners, from those who are just starting out and want to avoid overloading to the most experienced who are looking to fine-tune their preparation to the maximum. Knowing your SpO2 in real time can help you adjust the intensity of your workouts, prevent overtraining and adapt more safely to different altitudes.

Of course, it's not about making oxygenation the only relevant metric; supplementing it with heart rate, pace and personal feeling data is a very important part of getting a holistic view of your fitness. In the same way, any drastic drop in SpO2 can be a warning sign that can guide us about the need to rest or consult a professional, especially if it is accompanied by other symptoms.

Fortunately, we know that there are endless options of GPS heart rate monitors & sports watches that offer this functionality with optical sensor, but it is important to look at the accuracy, sampling rate and quality of the analysis platform. Only then can we get the most out of a metric that is certainly here to stay in our workouts.

So our motto should be something like...good running sensations always start with a body that gets the oxygen it needs!