My pulse oximeter displays both the heart rate and O2 saturation. Heart rate readings are useful enough. But what about O2 saturation? I'm thinking of cycling in particular, but I assume any benefits would translate easily to any kind of physical exercise.
O2 Saturation can, for the most part, be ignored.
If your O2 Saturation levels are low, then your lungs are not getting enough oxygen to your blood.
- Are you not breathing very much? You have to breath more when you exercise.
- Did you just complete a very hard exercise (like cycle to the top of a very large hill)? Your blood may have just used up a lot of oxygen doing that strenuous workout. Take a few moments to let your body recover by not exercising while your lungs send fresh oxygen through your body.
- Are you cycling in a confined area? If you are working out of your garage (stationary bicycle) and the car is running, that is not good! There may not be enough oxygen to keep you alive, and your O2 levels are definitely going to be dropping, because you are dying! Open the garage door, turn the car off, and step outside to get some fresh air.
That said, if you notice your Oxygen Saturation Levels dropping during a workout, you should seriously consider sitting down a moment to let your body recover or step outside to get some fresh air.
There could be people with medical conditions that need to monitor their blood's Oxygen levels, but for the most part this is not anything you are going to control on your own.
Blood oxygen saturation will go down slowly as exercise intensity goes up, then probably drop quickly to around or below 90% when you exceed maximum O2 intake (i.e. you can't breath any harder). At low spO2 values you will rapidly reach exhaustion. You can find articles on the subject on Livestrong or 3fatchicks.
The problem with LED-based oximeters is that they tend to not deal very well with motion artefacts. So during exercise you may end up with bad readings, held-up values or no value at all.
Heart rate tends to be easier to use as a physiological parameter when monitoring effort level.
Pulse Oximeters rely on arterial pulse flow at the capillary bed being sampled--typically your index finger. Accurate readings rely on how well your oximeter detects a pulse. I stopped using mine when hiking and biking because excessive movement, high ambient light outdoors on the probe area, and less flow at my finger tip (because more blood was being pumped to my legs?) made it difficult for the probe in my oximeter to detect a signal and thus ill-defined waveforms and readings I could not rely on.