Heart rate monitors have been the mainstay of ways to track our level of fitness and rate of recovery for quite some time now. From chest straps to fitness trackers and smart watches, or even the good old finger on the pulse technique. There are also very useful charts and guides letting us know how we stack up relative to our age, and importantly, how we measure up to our previous numbers.

But what about oxygen levels in the blood?

Every part of our body needs oxygen.1 We need it to turn food into fuel (cellular respiration). We need it to move muscles. We even need it to think.

When we move muscles during exercise we need more fuel, and oxygen is required to help produce that fuel (scientists call the fuel ATP), which is why our rate of breathing significantly increases when we’re active.

Simply put, the harder we exercise, the more oxygen we need to reach the muscles to convert glucose into a useable fuel (ATP). If there isn’t enough oxygen to generate the fuel, our body will make lactic acid for energy instead. But if the lactic acid levels build up in the bloodstream, we get a burning feeling in the muscles, which impacts our performance. It’s nature’s way of telling us to stop.2

High blood oxygen levels mean your body will transport oxygen throughout your body more quickly. If you have low blood oxygen levels, your body will send oxygen to your muscles at a much slower rate, which will affect your performance.

So, the level of oxygen in your blood is a very good indicator of your fitness. When we ‘run out of breath’, that’s our body telling us that our oxygen level has dropped.

That’s why keen runners and other athletes are adding blood oxygen to their list of metrics to measure and monitor their fitness. And yes, it means another gadget to buy – a Pulse Oximeter.

We love the A320 Pulse Oximeter by Heart Sure.


Pulse oximeter on finger

What is a pulse oximeter and how does it work?

A pulse oximeter measures blood oxygen levels (oxygen saturation or SpO2).

When oxygen is taken into the lungs, it is transferred into the bloodstream and attaches to a protein in the red blood cells called haemoglobin. The red blood cells then transport the oxygen to where it’s needed.3

A pulse oximeter is a small device that usually clips onto your finger and passes light through one side of your finger onto a light detector on the other side. As it passes through your finger, the light hits your blood cells and reacts differently to the cells carrying oxygen, compared to the cells not carrying oxygen. The characteristics of the light that makes it to the photodetector tells you how much oxygen is in your blood.

So, back to the original question – does blood oxygen level drop during exercise – yes it does, simply because of the extra demands of the muscles.

When you’re not exercising, the oxygen saturation level is between 95% and 99%.

Ideally that level should stay above 92% during exercise to keep the proper pressure of oxygen in the blood.


Always read & follow the instructions for use & health warnings. Consult your health professional to evaluate the readings.


  1. https://www.blf.org.uk/support-for-you/how-your-lungs-work/why-do-we-breathe
  2. https://www.webmd.com/fitness-exercise/guide/exercise-and-lactic-acidosis#1
  3. https://www.frontiersin.org/articles/10.3389/fphys.2013.00332/full
  4. https://exercise.lovetoknow.com/about-physical-fitness/understanding-blood-oxygen-levels-during-exercise