Here’s an indoor run from a Humon athlete. He put his Hex on when he arrived at the gym and jumped on the treadmill immediately. When he started running, you can see the muscle oxygen level (SmO2) drops initially. This usually indicates that the muscles are contracting and less oxygen (O2) is available. But as he continues to run, the SmO2 goes up since the blood flow is starting to increase and supply the muscles with more O2.
As he continues to run at this fast pace, you can see the SmO2 starts to drop. He hits an orange zone around minute 16, which means his oxygen consumption is beginning to exceed the oxygen supply. He even hits a bit of a red zone. But then his muscle goes back to the green zone even though SmO2 is still dropping…why is that?
SmO2 is a balance between oxygen supply and demand in the muscle. So even at times when you’re pushing super hard, you may still be in a ”steady state” because the blood is supplying more O2 to the muscles to keep up with what is needed.
The hemoglobin concentration in the muscle can be seen in the Hemoglobin Concentration plot below. It is important to remember that within this hemoglobin signal, there is contributions from hemoglobin that carries oxygen (HbO2) (since the O2 is picked up from the lungs!) and hemoglobin that has no oxygen (Hb) (since the O2 been delivered to tissue that required energy!)
Look at the Hemoglobin Concentration plot around minute 25. The hemoglobin concentration starts to rise rapidly and therefore the SmO2 returns to a steady state since the muscles have found a way to adjust to this high intensity.
However, around minute 40, the SmO2 drops even further and the hemoglobin concentration can no longer increase quickly enough. Therefore, that is a pace he can no longer sustain.
NOTE: Hemoglobin concentration is currently being recorded by the Hex, just not displayed on this app. We'll be releasing an update soon so you can see the hemoglobin concentration!
** REMEMBER the hemoglobin concentration values represent relative changes - check out more information here.