so his other point he makes on NIRS info:
” So, the BSXinsight Gen2 SmO2 is calibrated for absolute measurements within a range from 0% to 100%, where 0% indicates that all hemoglobin in the tissue volume directly below the sensor have completely given out their oxygen and, thus, consist of deoxyhemoglobin, while 100% indicates that all hemoglobin in the tissue directly below the sensor are oxygenated (oxyhemoglobin). ”
is somewhat in a contradiction. I do not know how BSX exactly works but all other NIRS equipment when they show low or zero clearly do not have zero O2Hb. a low number simply means allow pO2 pressure as well a limitation from the technology. . Remember NIRS does not make a difference between Mb and Hb O2 loading so unlikely is zero a zero value but a limitation of the ability to read very low levels of O2 on Hb and or Mb. It is less a personal believe but a fact based on some great studies and research . Here a very short part of one of the leading groups on this.
“Richardson et al have concluded that: ‘‘…intracellular pO2 remains constant during graded incremental exercise in humans (50–100% of muscle VO2max)’’ so that: ‘‘With respect to the concept of the ‘‘anaerobic’’ threshold, these data demonstrate that, during incremental exercise, skeletal muscle cells do not become anaerobic as lactate levels suddenly rise, as intracellular pO2 is well preserved at a constant level, even at maximal exercise’’ (p. 63168). They also conclude that: ‘‘Net blood lactate efflux was unrelated to intracellular pO2 across the range of incremental exercise to
exhaustion’’ but was ‘‘linearly related to O2 consumption’’ (p. 62768). Another study confirmed these conclusions: ‘‘…consequently these data again demonstrate that, as assessed by cytosolic oxygenation state (deoxy-Mb) during incremental exercise, skeletal muscle cells do not become ‘‘anaerobic’’ as lactate levels rise, because intracellular PO2 is well preserved
at a low but constant level even at maximal exercise’’”
Now as Adam showed nicely with a occlusion test the values in BSX drop down to very low levels indicating , which is not surprising that they use a NIRS technology.
So as he points out
” So, just think about that, when setting your range expectations.”
But you have to understand, if we fudged the numbers to make them look better, those who rightfully want to see absolute, would be very disappointed..
Absolutely agree and great point made and it is important for newcomer in this bio feedback ideas to get some pointer in this directions. So I like to make a super simplistic feedback on here to show you what you or when you can expect some lower or less lower numbers.
A artificial occlusion test is really a “forced” delivery problem.
meaning , that I stop O2 delivery to the working or O2 needed area and as such the cells in this are will have to take on what is already there.. So that is what D Adam explains nicely the O2 need of any cell and the reason why we see SmO2 dropping to a very low even zero level depending how the NIRS can get absorb or reflect. I will show a nice occlusion test with BSX and MOXY at the end done on the same muscle so all the same conditions and it shows NIRS works nicely no matter on the name or brand.
Now in a 6 min occlusion test, which is what is done during research due to risks involved we can assume if the occlusion is properly done, that we have very to no O2 inflow and we use from Mb and HB O2 as long as possible. Now the fun part is that we do nothing and have no blood flow. so we are basically on a resting metabolic energy consumption. Now there are nice formulas under occlusion, where we can calculated the amount of energy or O2 used..
In this simplistic case, we assume the whole body is under occlusion so we have no O2 supply anymore.
Resting metabolic rate may be 1800 kcal/ 24 hours so we have 75 kcal / h or during occlusion situation of 6 min we use about 7.5kcal /h.
No NIRS equipment will show very low levels of SmO2 as shown in occlusion tests.
Now we do an activity . first . . If we increase the load slowly we give the delivery systems time to react to the O2 demand and as such many will be surprised, that in a VO2 max test or a 3 min LT step test the SmO2 values do not go very low depending on limiter and or compensators.
But if you do a Wingate test you will see a similar low level like in a occlusion test. This is for many surprising as a wingate is a typical classical anaerobic assessment but with NIRS it shows , that O2 use is higher per time in a Wingate than in a VO2 test. For all the great critics on here, there are many publications in accepted papers who show this results.
So lets go back to why we can see very low levels in NIRS assisted workouts.
Let’s do a ride and push a short hill up all out for 30 seconds.. You go to the base of the hill with a HR of 120 as SV of 120 so CO of 14.4 L / min
So approximately 3 x higher than in your resting occlusion test where you may had a HR of 60 and a SV of 80
Now at rest in the occlusion situation your capillarisation is relative sleepy and you just move the O2 needed to keep every body happy in the tested area which may be 50 – 70 % of SmO2 values
In the beginning of the hill situation you will have in most cases a much higher SmO2 so the resting SmO2 will increase..
The highest values you may see are depending on the equipment somewhere between 90 – 95 %( There are many factors who avoid 100 % readings.
Now you push up the hill suddenly so delivery system will be surprised and you create a natural delivery problem which is close to the artificial occlusion created delivery problem.
Now 30 seconds all out . Your working metabolic rate in a 1 hours all out can easy be 1800 kcal / h ( and that is NOT all out ) so 1800 in 60 min will give you 30 kcal in 1 min or in 6 seconds , the duration of the occlusion we are down to 5 kcal
This moves us relative close to the same situation a sin an occlusion test and that’s’ why when we use NIRS we can see tsi very low numbers in a workout depending what wee do. There are than some other very intriguing options left for the body to react.
So to support Adams point
“So, just think about that, when setting your range expectations.” ” if we fudged the numbers to make them look better, those who rightfully want to see absolute, would be very disappointed.
Adam great points and absolutely agree. And here for all NIRS sceptics a occlusion test sent to us from a MOXY and BSX user Thanks so much