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Development Team Member
Posts: 59
I have observed that SmO2 readings can vary a lot
depending on the positioning of the sensor. I put
a sensor on my quadriceps: vastus lateralis.

What is the best way to ensure consistency
between training sessions?

I am concerned that if I position the sensor 
in a different position by a few centimeters
that it will be hard to compare SmO2 readings
between different sessions and/or monitor 


Development Team Member
Posts: 1,501
Absolutely   look  at the many posts on this in the forum. but great observation.

Posts: 265
In my experience, you will often see different responses on different muscles so you should be aware of which muscle you are measuring.  You will sometimes see a different value by just moving to a different position on the same muscle. On myself, I often get a few % lower SmO2 on the VL closer to the knee compared to having the sensor halfway between the knee and hip.  However, the trend response is the same for a given muscle.

Also, you will tend to get more stable readings while exercising.  At rest, the oxygen supply is very small and the oxygen utilization is very small.  So small changes in either one can make a big change in SmO2.  Tensing or relaxing the muscle for several seconds can be enough to induce a change.  When you are checking position sensitivity at rest you need to make sure that your posture doesn't change when you move the sensor and that your SmO2 is stable.  It's good to move back and forth between the locations several times to ensure that the difference is really due to the location.

Some researchers do place a small pen mark on the skin to help get the sensor precisely in the same spot but this isn't usually necessary.  If you find the muscle you are targeting and then place it on the middle of the belly of the muscle, you should be fine.

Here's a post from ryinc where he repeated a test on himself a couple of weeks apart.

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